diff --git a/chrome/src/nsChromeProtocolHandler.cpp b/chrome/src/nsChromeProtocolHandler.cpp
index 7df3fa80603..16c36a7a0ea 100644
--- a/chrome/src/nsChromeProtocolHandler.cpp
+++ b/chrome/src/nsChromeProtocolHandler.cpp
@@ -245,11 +245,45 @@ nsChromeProtocolHandler::NewChannel(nsIURI* aURI,
         result->SetOwner(owner);
     }
 
-    // XXX Removed dependency-tracking code from here, because we're not
-    // tracking them anyways (with fastload we checked only in DEBUG
-    // and with startupcache not at all), but this is where we would start
-    // if we need to re-add.
-    // See bug 531886, bug 533038.
+#ifdef MOZ_XUL
+    // Track FastLoad file dependencies.
+    //
+    // This is harder than it ought to be!  While an nsResChannel "is-a"
+    // nsIFileChannel, an nsJARChannel is not.  Once you unravel the jar:
+    // URI, you may have a resource: URL -- but without a channel for it,
+    // you can't get the URI that it yields through substitution!
+    //
+    // XXXbe fix nsResChannel.cpp to move the substitution code into a new
+    //       nsResURL class?
+    nsCOMPtr<nsIFastLoadService> fastLoadServ(do_GetFastLoadService());
+    if (fastLoadServ) {
+        nsCOMPtr<nsIObjectOutputStream> objectOutput;
+        fastLoadServ->GetOutputStream(getter_AddRefs(objectOutput));
+        if (objectOutput) {
+            nsCOMPtr<nsIFile> file;
+
+            nsCOMPtr<nsIURI> uri;
+            result->GetURI(getter_AddRefs(uri));
+            uri = NS_GetInnermostURI(uri);
+
+            // Here we have a URL of the form resource:/chrome/A.jar
+            // or file:/some/path/to/A.jar.
+            nsCOMPtr<nsIFileURL> fileURL(do_QueryInterface(uri));
+            if (fileURL)
+                fileURL->GetFile(getter_AddRefs(file));
+
+            if (file) {
+                rv = fastLoadServ->AddDependency(file);
+                if (NS_FAILED(rv)) {
+                   nsCOMPtr<nsIXULPrototypeCache> cache
+                       (do_GetService(kXULPrototypeCacheCID));
+                   if (cache)
+                       cache->AbortFastLoads();
+                }
+            }
+        }
+    }
+#endif
 
     *aResult = result;
     NS_ADDREF(*aResult);
diff --git a/content/xul/content/src/nsXULElement.cpp b/content/xul/content/src/nsXULElement.cpp
index ec1a355be13..e80efb5e1fd 100644
--- a/content/xul/content/src/nsXULElement.cpp
+++ b/content/xul/content/src/nsXULElement.cpp
@@ -84,6 +84,7 @@
 #include "nsIEventListenerManager.h"
 #include "nsEventStateManager.h"
 #include "nsFocusManager.h"
+#include "nsIFastLoadService.h"
 #include "nsHTMLStyleSheet.h"
 #include "nsINameSpaceManager.h"
 #include "nsIObjectInputStream.h"
@@ -2687,9 +2688,9 @@ nsXULPrototypeElement::Serialize(nsIObjectOutputStream* aStream,
 
                 if (script->mScriptObject.mObject) {
                     // This may return NS_OK without muxing script->mSrcURI's
-                    // data into the cache file, in the case where that
+                    // data into the FastLoad file, in the case where that
                     // muxed document is already there (written by a prior
-                    // session, or by an earlier cache episode during this
+                    // session, or by an earlier FastLoad episode during this
                     // session).
                     rv |= script->SerializeOutOfLine(aStream, aGlobal);
                 }
@@ -2819,8 +2820,8 @@ nsXULPrototypeElement::Deserialize(nsIObjectInputStream* aStream,
 
             // Oh dear. Something failed during the deserialization.
             // We don't know what.  But likely consequences of failed
-            // deserializations included calls to |AbortCaching| which
-            // shuts down the cache and closes our streams.
+            // deserializations included calls to |AbortFastLoads| which
+            // shuts down the FastLoadService and closes our streams.
             // If that happens, next time through this loop, we die a messy
             // death. So, let's just fail now, and propagate that failure
             // upward so that the ChromeProtocolHandler knows it can't use
@@ -2960,23 +2961,24 @@ nsresult
 nsXULPrototypeScript::SerializeOutOfLine(nsIObjectOutputStream* aStream,
                                          nsIScriptGlobalObject* aGlobal)
 {
-    nsresult rv = NS_ERROR_NOT_IMPLEMENTED;
-
-    PRBool isChrome = PR_FALSE;
-    if (NS_FAILED(mSrcURI->SchemeIs("chrome", &isChrome)) || !isChrome)
-       // Don't cache scripts that don't come from chrome uris.
-       return rv;
-
     nsXULPrototypeCache* cache = nsXULPrototypeCache::GetInstance();
     if (!cache)
         return NS_ERROR_OUT_OF_MEMORY;
 
     NS_ASSERTION(cache->IsEnabled(),
-                 "writing to the cache file, but the XUL cache is off?");
-    PRBool exists;
-    cache->HasData(mSrcURI, &exists);
-    
-    
+                 "writing to the FastLoad file, but the XUL cache is off?");
+
+    nsIFastLoadService* fastLoadService = cache->GetFastLoadService();
+    if (!fastLoadService)
+        return NS_ERROR_NOT_AVAILABLE;
+
+    nsCAutoString urispec;
+    nsresult rv = mSrcURI->GetAsciiSpec(urispec);
+    if (NS_FAILED(rv))
+        return rv;
+
+    PRBool exists = PR_FALSE;
+    fastLoadService->HasMuxedDocument(urispec.get(), &exists);
     /* return will be NS_OK from GetAsciiSpec.
      * that makes no sense.
      * nor does returning NS_OK from HasMuxedDocument.
@@ -2985,15 +2987,34 @@ nsXULPrototypeScript::SerializeOutOfLine(nsIObjectOutputStream* aStream,
     if (exists)
         return NS_OK;
 
-    nsCOMPtr<nsIObjectOutputStream> oos;
-    rv = cache->GetOutputStream(mSrcURI, getter_AddRefs(oos));
-    NS_ENSURE_SUCCESS(rv, rv);
-    
-    rv |= Serialize(oos, aGlobal, nsnull);
-    rv |= cache->FinishOutputStream(mSrcURI);
+    // Allow callers to pass null for aStream, meaning
+    // "use the FastLoad service's default output stream."
+    // See nsXULDocument.cpp for one use of this.
+    nsCOMPtr<nsIObjectOutputStream> objectOutput = aStream;
+    if (! objectOutput) {
+        fastLoadService->GetOutputStream(getter_AddRefs(objectOutput));
+        if (! objectOutput)
+            return NS_ERROR_NOT_AVAILABLE;
+    }
+
+    rv = fastLoadService->
+         StartMuxedDocument(mSrcURI, urispec.get(),
+                            nsIFastLoadService::NS_FASTLOAD_WRITE);
+    NS_ASSERTION(rv != NS_ERROR_NOT_AVAILABLE, "reading FastLoad?!");
+
+    nsCOMPtr<nsIURI> oldURI;
+    rv |= fastLoadService->SelectMuxedDocument(mSrcURI, getter_AddRefs(oldURI));
+    rv |= Serialize(objectOutput, aGlobal, nsnull);
+    rv |= fastLoadService->EndMuxedDocument(mSrcURI);
+
+    if (oldURI) {
+        nsCOMPtr<nsIURI> tempURI;
+        rv |= fastLoadService->
+              SelectMuxedDocument(oldURI, getter_AddRefs(tempURI));
+    }
 
     if (NS_FAILED(rv))
-        cache->AbortCaching();
+        cache->AbortFastLoads();
     return rv;
 }
 
@@ -3034,24 +3055,33 @@ nsresult
 nsXULPrototypeScript::DeserializeOutOfLine(nsIObjectInputStream* aInput,
                                            nsIScriptGlobalObject* aGlobal)
 {
-    // Keep track of failure via rv, so we can
-    // AbortCaching if things look bad.
+    // Keep track of FastLoad failure via rv, so we can
+    // AbortFastLoads if things look bad.
     nsresult rv = NS_OK;
+
     nsXULPrototypeCache* cache = nsXULPrototypeCache::GetInstance();
-  
+    nsIFastLoadService* fastLoadService = cache->GetFastLoadService();
+
+    // Allow callers to pass null for aInput, meaning
+    // "use the FastLoad service's default input stream."
+    // See nsXULContentSink.cpp for one use of this.
     nsCOMPtr<nsIObjectInputStream> objectInput = aInput;
-    if (cache) {
+    if (! objectInput && fastLoadService)
+        fastLoadService->GetInputStream(getter_AddRefs(objectInput));
+
+    if (objectInput) {
         PRBool useXULCache = PR_TRUE;
         if (mSrcURI) {
             // NB: we must check the XUL script cache early, to avoid
-            // multiple deserialization attempts for a given script.            
-            // Note that nsXULDocument::LoadScript
+            // multiple deserialization attempts for a given script, which
+            // would exhaust the multiplexed stream containing the singly
+            // serialized script.  Note that nsXULDocument::LoadScript
             // checks the XUL script cache too, in order to handle the
             // serialization case.
             //
             // We need do this only for <script src='strres.js'> and the
             // like, i.e., out-of-line scripts that are included by several
-            // different XUL documents stored in the cache file.
+            // different XUL documents multiplexed in the FastLoad file.
             useXULCache = cache->IsEnabled();
 
             if (useXULCache) {
@@ -3075,21 +3105,47 @@ nsXULPrototypeScript::DeserializeOutOfLine(nsIObjectInputStream* aInput,
         }
 
         if (! mScriptObject.mObject) {
+            nsCOMPtr<nsIURI> oldURI;
+
             if (mSrcURI) {
-                rv = cache->GetInputStream(mSrcURI, getter_AddRefs(objectInput));
-            } 
-            // If !mSrcURI, we have an inline script. We shouldn't have 
-            // to do anything else in that case, I think.
- 
+                nsCAutoString spec;
+                mSrcURI->GetAsciiSpec(spec);
+                rv = fastLoadService->StartMuxedDocument(mSrcURI, spec.get(),
+                                                         nsIFastLoadService::NS_FASTLOAD_READ);
+                if (NS_SUCCEEDED(rv))
+                    rv = fastLoadService->SelectMuxedDocument(mSrcURI, getter_AddRefs(oldURI));
+            } else {
+                // An inline script: check FastLoad multiplexing direction
+                // and skip Deserialize if we're not reading from a
+                // muxed stream to get inline objects that are contained in
+                // the current document.
+                PRInt32 direction;
+                fastLoadService->GetDirection(&direction);
+                if (direction != nsIFastLoadService::NS_FASTLOAD_READ)
+                    rv = NS_ERROR_NOT_AVAILABLE;
+            }
+
             // We do reflect errors into rv, but our caller may want to
             // ignore our return value, because mScriptObject will be null
             // after any error, and that suffices to cause the script to
             // be reloaded (from the src= URI, if any) and recompiled.
             // We're better off slow-loading than bailing out due to a
-            // error.
+            // FastLoad error.
             if (NS_SUCCEEDED(rv))
                 rv = Deserialize(objectInput, aGlobal, nsnull, nsnull);
 
+            if (NS_SUCCEEDED(rv) && mSrcURI) {
+                rv = fastLoadService->EndMuxedDocument(mSrcURI);
+
+                if (NS_SUCCEEDED(rv) && oldURI) {
+                    nsCOMPtr<nsIURI> tempURI;
+                    rv = fastLoadService->SelectMuxedDocument(oldURI, getter_AddRefs(tempURI));
+
+                    NS_ASSERTION(NS_SUCCEEDED(rv) && (!tempURI || tempURI == mSrcURI),
+                                 "not currently deserializing into the script we thought we were!");
+                }
+            }
+
             if (NS_SUCCEEDED(rv)) {
                 if (useXULCache && mSrcURI) {
                     PRBool isChrome = PR_FALSE;
@@ -3100,17 +3156,17 @@ nsXULPrototypeScript::DeserializeOutOfLine(nsIObjectInputStream* aInput,
                                          mScriptObject.mObject);
                     }
                 }
-                cache->FinishInputStream(mSrcURI);
             } else {
-                // If mSrcURI is not in the cache,
+                // If mSrcURI is not in the FastLoad multiplex,
                 // rv will be NS_ERROR_NOT_AVAILABLE and we'll try to
-                // update the cache file to hold a serialization of
+                // update the FastLoad file to hold a serialization of
                 // this script, once it has finished loading.
                 if (rv != NS_ERROR_NOT_AVAILABLE)
-                    cache->AbortCaching();
+                    cache->AbortFastLoads();
             }
         }
     }
+
     return rv;
 }
 
diff --git a/content/xul/document/public/nsIXULPrototypeCache.h b/content/xul/document/public/nsIXULPrototypeCache.h
index ba34f29c508..f9304a08527 100644
--- a/content/xul/document/public/nsIXULPrototypeCache.h
+++ b/content/xul/document/public/nsIXULPrototypeCache.h
@@ -65,9 +65,9 @@ public:
     virtual PRBool IsCached(nsIURI* aURI) = 0;
 
     /**
-     * Stop the caching process abruptly, removing the cache file.
+     * Stop the FastLoad process abruptly, removing the FastLoad file.
      */
-    virtual void AbortCaching() = 0;
+    virtual void AbortFastLoads() = 0;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(nsIXULPrototypeCache, NS_IXULPROTOTYPECACHE_IID)
diff --git a/content/xul/document/src/nsXULDocument.cpp b/content/xul/document/src/nsXULDocument.cpp
index 02cbfbec238..6ffe838aa2e 100644
--- a/content/xul/document/src/nsXULDocument.cpp
+++ b/content/xul/document/src/nsXULDocument.cpp
@@ -289,11 +289,12 @@ nsXULDocument::~nsXULDocument()
         NS_IF_RELEASE(kNC_attribute);
         NS_IF_RELEASE(kNC_value);
 
-        // Remove the current document here from the table in
+        // Remove the current document here from the FastLoad table in
         // case the document did not make it past StartLayout in
-        // ResumeWalk. 
+        // ResumeWalk. The FastLoad table must be clear of entries so
+        // that the FastLoad file footer can be properly written.
         if (mDocumentURI)
-            nsXULPrototypeCache::GetInstance()->RemoveFromCacheSet(mDocumentURI);
+            nsXULPrototypeCache::GetInstance()->RemoveFromFastLoadSet(mDocumentURI);
     }
 }
 
@@ -450,7 +451,7 @@ nsXULDocument::SetContentType(const nsAString& aContentType)
 }
 
 // This is called when the master document begins loading, whether it's
-// being cached or not.
+// fastloaded or not.
 nsresult
 nsXULDocument::StartDocumentLoad(const char* aCommand, nsIChannel* aChannel,
                                  nsILoadGroup* aLoadGroup,
@@ -493,9 +494,9 @@ nsXULDocument::StartDocumentLoad(const char* aCommand, nsIChannel* aChannel,
     // to trigger the fail-safe parse-from-disk solution. Example failure cases
     // (for reference) include:
     //
-    // NS_ERROR_NOT_AVAILABLE: the URI cannot be found in the startup cache,
+    // NS_ERROR_NOT_AVAILABLE: the URI cannot be found in the FastLoad cache,
     //                         parse from disk
-    // other: the startup cache file could not be found, probably
+    // other: the FastLoad cache file, XUL.mfl, could not be found, probably
     //        due to being accessed before a profile has been selected (e.g.
     //        loading chrome for the profile manager itself). This must be
     //        parsed from disk.
diff --git a/content/xul/document/src/nsXULPrototypeCache.cpp b/content/xul/document/src/nsXULPrototypeCache.cpp
index 018f4edc820..854badba7cc 100644
--- a/content/xul/document/src/nsXULPrototypeCache.cpp
+++ b/content/xul/document/src/nsXULPrototypeCache.cpp
@@ -57,8 +57,6 @@
 #include "nsIObjectInputStream.h"
 #include "nsIObjectOutputStream.h"
 #include "nsIObserverService.h"
-#include "nsIStringStream.h"
-#include "nsIStorageStream.h"
 
 #include "nsNetUtil.h"
 #include "nsAppDirectoryServiceDefs.h"
@@ -66,17 +64,13 @@
 #include "jsxdrapi.h"
 
 #include "mozilla/Preferences.h"
-#include "mozilla/scache/StartupCache.h"
-#include "mozilla/scache/StartupCacheUtils.h"
 
 using namespace mozilla;
-using namespace mozilla::scache;
 
 static NS_DEFINE_CID(kXULPrototypeCacheCID, NS_XULPROTOTYPECACHE_CID);
 
 static PRBool gDisableXULCache = PR_FALSE; // enabled by default
 static const char kDisableXULCachePref[] = "nglayout.debug.disable_xul_cache";
-static const char kXULCacheInfoKey[] = "nsXULPrototypeCache.startupCache";
 
 //----------------------------------------------------------------------
 
@@ -96,7 +90,9 @@ DisableXULCacheChangedCallback(const char* aPref, void* aClosure)
 
 //----------------------------------------------------------------------
 
-StartupCache*   nsXULPrototypeCache::gStartupCache = nsnull;
+
+nsIFastLoadService*   nsXULPrototypeCache::gFastLoadService = nsnull;
+nsIFile*              nsXULPrototypeCache::gFastLoadFile = nsnull;
 nsXULPrototypeCache*  nsXULPrototypeCache::sInstance = nsnull;
 
 
@@ -108,6 +104,9 @@ nsXULPrototypeCache::nsXULPrototypeCache()
 nsXULPrototypeCache::~nsXULPrototypeCache()
 {
     FlushScripts();
+
+    NS_IF_RELEASE(gFastLoadService); // don't need ReleaseService nowadays!
+    NS_IF_RELEASE(gFastLoadFile);
 }
 
 
@@ -130,13 +129,8 @@ NS_NewXULPrototypeCache(nsISupports* aOuter, REFNSIID aIID, void** aResult)
     if (!(result->mPrototypeTable.Init() &&
           result->mStyleSheetTable.Init() &&
           result->mScriptTable.Init() &&
-          result->mXBLDocTable.Init())) {
-        return NS_ERROR_OUT_OF_MEMORY;
-    }
-
-    if (!(result->mCacheURITable.Init() &&
-          result->mInputStreamTable.Init() &&
-          result->mOutputStreamTable.Init())) {
+          result->mXBLDocTable.Init() &&
+          result->mFastLoadURITable.Init())) {
         return NS_ERROR_OUT_OF_MEMORY;
     }
 
@@ -175,10 +169,10 @@ nsXULPrototypeCache::GetInstance()
     return sInstance;
 }
 
-/* static */ StartupCache*
-nsXULPrototypeCache::GetStartupCache()
+/* static */ nsIFastLoadService*
+nsXULPrototypeCache::GetFastLoadService()
 {
-    return gStartupCache;
+    return gFastLoadService;
 }
 
 //----------------------------------------------------------------------
@@ -195,7 +189,7 @@ nsXULPrototypeCache::Observe(nsISupports* aSubject,
         Flush();
     }
     else if (!strcmp(aTopic, "startupcache-invalidate")) {
-        AbortCaching();
+        AbortFastLoads();
     }
     else {
         NS_WARNING("Unexpected observer topic.");
@@ -207,34 +201,42 @@ nsXULPrototypeDocument*
 nsXULPrototypeCache::GetPrototype(nsIURI* aURI)
 {
     nsXULPrototypeDocument* protoDoc = mPrototypeTable.GetWeak(aURI);
-    if (protoDoc)
-        return protoDoc;
 
-    nsresult rv = BeginCaching(aURI);
-    if (NS_FAILED(rv))
-        return nsnull;
+    if (!protoDoc) {
+        // No prototype in XUL memory cache. Spin up FastLoad Service and
+        // look in FastLoad file.
+        nsresult rv = StartFastLoad(aURI);
+        if (NS_SUCCEEDED(rv)) {
+            nsCOMPtr<nsIObjectInputStream> objectInput;
+            gFastLoadService->GetInputStream(getter_AddRefs(objectInput));
 
-    // No prototype in XUL memory cache. Spin up the cache Service.
-    nsCOMPtr<nsIObjectInputStream> ois;
-    rv = GetInputStream(aURI, getter_AddRefs(ois));
-    if (NS_FAILED(rv))
-        return nsnull;
-    
-    nsRefPtr<nsXULPrototypeDocument> newProto;
-    rv = NS_NewXULPrototypeDocument(getter_AddRefs(newProto));
-    if (NS_FAILED(rv))
-        return nsnull;
-    
-    rv = newProto->Read(ois);
-    if (NS_SUCCEEDED(rv)) {
-        rv = PutPrototype(newProto);
-    } else {
-        newProto = nsnull;
+            rv = StartFastLoadingURI(aURI, nsIFastLoadService::NS_FASTLOAD_READ);
+            if (NS_SUCCEEDED(rv)) {
+                nsCOMPtr<nsIURI> oldURI;
+                gFastLoadService->SelectMuxedDocument(aURI, getter_AddRefs(oldURI));
+
+                // Create a new prototype document.
+                nsRefPtr<nsXULPrototypeDocument> newProto;
+                rv = NS_NewXULPrototypeDocument(getter_AddRefs(newProto));
+                if (NS_FAILED(rv)) return nsnull;
+
+                rv = newProto->Read(objectInput);
+                if (NS_SUCCEEDED(rv)) {
+                    rv = PutPrototype(newProto);
+                    if (NS_FAILED(rv))
+                        newProto = nsnull;
+
+                    gFastLoadService->EndMuxedDocument(aURI);
+                } else {
+                    newProto = nsnull;
+                }
+
+                RemoveFromFastLoadSet(aURI);
+                protoDoc = newProto;
+            }
+        }
     }
-    
-    mInputStreamTable.Remove(aURI);
-    RemoveFromCacheSet(aURI);
-    return newProto;
+    return protoDoc;
 }
 
 nsresult
@@ -403,10 +405,11 @@ nsXULPrototypeCache::IsEnabled()
     return !gDisableXULCache;
 }
 
-static PRBool gDisableXULDiskCache = PR_FALSE;           // enabled by default
+static PRBool gDisableXULFastLoad = PR_FALSE;           // enabled by default
+static PRBool gChecksumXULFastLoadFile = PR_TRUE;       // XXXbe too paranoid
 
 void
-nsXULPrototypeCache::AbortCaching()
+nsXULPrototypeCache::AbortFastLoads()
 {
 #ifdef DEBUG_brendan
     NS_BREAK();
@@ -416,187 +419,282 @@ nsXULPrototypeCache::AbortCaching()
     // script, somehow.
     Flush();
 
-    // Clear the cache set
-    mCacheURITable.Clear();
+    // Clear the FastLoad set
+    mFastLoadURITable.Clear();
+
+    nsCOMPtr<nsIFastLoadService> fastLoadService = gFastLoadService;
+    nsCOMPtr<nsIFile> file = gFastLoadFile;
+
+    nsresult rv;
+
+    if (! fastLoadService) {
+        fastLoadService = do_GetFastLoadService();
+        if (! fastLoadService)
+            return;
+
+        rv = fastLoadService->NewFastLoadFile(XUL_FASTLOAD_FILE_BASENAME,
+                                              getter_AddRefs(file));
+        if (NS_FAILED(rv))
+            return;
+    }
+
+    // Fetch the current input (if FastLoad file existed) or output (if we're
+    // creating the FastLoad file during this app startup) stream.
+    nsCOMPtr<nsIObjectInputStream> objectInput;
+    nsCOMPtr<nsIObjectOutputStream> objectOutput;
+    fastLoadService->GetInputStream(getter_AddRefs(objectInput));
+    fastLoadService->GetOutputStream(getter_AddRefs(objectOutput));
+
+    if (objectOutput) {
+        fastLoadService->SetOutputStream(nsnull);
+
+        if (NS_SUCCEEDED(objectOutput->Close()) && gChecksumXULFastLoadFile)
+            fastLoadService->CacheChecksum(file,
+                                           objectOutput);
+    }
+
+    if (objectInput) {
+        // If this is the last of one or more XUL master documents loaded
+        // together at app startup, close the FastLoad service's singleton
+        // input stream now.
+        fastLoadService->SetInputStream(nsnull);
+        objectInput->Close();
+    }
+
+    // Now rename or remove the file.
+    if (file) {
+#ifdef DEBUG
+        // Remove any existing Aborted.mfasl files generated in previous runs.
+        nsCOMPtr<nsIFile> existingAbortedFile;
+        file->Clone(getter_AddRefs(existingAbortedFile));
+        if (existingAbortedFile) {
+            existingAbortedFile->SetLeafName(NS_LITERAL_STRING("Aborted.mfasl"));
+            PRBool fileExists = PR_FALSE;
+            existingAbortedFile->Exists(&fileExists);
+            if (fileExists)
+                existingAbortedFile->Remove(PR_FALSE);
+        }
+        file->MoveToNative(nsnull, NS_LITERAL_CSTRING("Aborted.mfasl"));
+#else
+        rv = file->Remove(PR_FALSE);
+        if (NS_FAILED(rv))
+            NS_WARNING("Failed to remove fastload file, fastload data may be outdated");
+#endif
+    }
+
+    // If the list is empty now, the FastLoad process is done.
+    NS_IF_RELEASE(gFastLoadService);
+    NS_IF_RELEASE(gFastLoadFile);
 }
 
 
-static const char kDisableXULDiskCachePref[] = "nglayout.debug.disable_xul_fastload";
-
 void
-nsXULPrototypeCache::RemoveFromCacheSet(nsIURI* aURI)
+nsXULPrototypeCache::RemoveFromFastLoadSet(nsIURI* aURI)
 {
-    mCacheURITable.Remove(aURI);
+    mFastLoadURITable.Remove(aURI);
 }
 
+static const char kDisableXULFastLoadPref[] = "nglayout.debug.disable_xul_fastload";
+static const char kChecksumXULFastLoadFilePref[] = "nglayout.debug.checksum_xul_fastload_file";
+
 nsresult
 nsXULPrototypeCache::WritePrototype(nsXULPrototypeDocument* aPrototypeDocument)
 {
     nsresult rv = NS_OK, rv2 = NS_OK;
 
-    // We're here before the startupcache service has been initialized, probably because
+    // We're here before the FastLoad service has been initialized, probably because
     // of the profile manager. Bail quietly, don't worry, we'll be back later.
-    if (!gStartupCache)
+    if (! gFastLoadService)
         return NS_OK;
 
+    // Fetch the current input (if FastLoad file existed) or output (if we're
+    // creating the FastLoad file during this app startup) stream.
+    nsCOMPtr<nsIObjectInputStream> objectInput;
+    nsCOMPtr<nsIObjectOutputStream> objectOutput;
+    gFastLoadService->GetInputStream(getter_AddRefs(objectInput));
+    gFastLoadService->GetOutputStream(getter_AddRefs(objectOutput));
+
     nsCOMPtr<nsIURI> protoURI = aPrototypeDocument->GetURI();
 
-    // Remove this document from the cache table. We use the table's
-    // emptiness instead of a counter to decide when the caching process 
-    // has completed.
-    RemoveFromCacheSet(protoURI);
+    // Remove this document from the FastLoad table. We use the table's
+    // emptiness instead of a counter to decide when the FastLoad process
+    // has completed. When complete, we can write footer details to the
+    // FastLoad file.
+    RemoveFromFastLoadSet(protoURI);
 
-    PRInt32 count = mCacheURITable.Count();
-    nsCOMPtr<nsIObjectOutputStream> oos;
-    rv = GetOutputStream(protoURI, getter_AddRefs(oos));
-    NS_ENSURE_SUCCESS(rv, rv);
+    PRInt32 count = mFastLoadURITable.Count();
+
+    if (objectOutput) {
+        rv = StartFastLoadingURI(protoURI, nsIFastLoadService::NS_FASTLOAD_WRITE);
+        if (NS_SUCCEEDED(rv)) {
+            // Re-select the URL of the current prototype, as out-of-line script loads
+            // may have changed
+            nsCOMPtr<nsIURI> oldURI;
+            gFastLoadService->SelectMuxedDocument(protoURI, getter_AddRefs(oldURI));
+
+            aPrototypeDocument->Write(objectOutput);
+
+            gFastLoadService->EndMuxedDocument(protoURI);
+        }
+
+        // If this is the last of one or more XUL master documents loaded
+        // together at app startup, close the FastLoad service's singleton
+        // output stream now.
+        //
+        // NB: we must close input after output, in case the output stream
+        // implementation needs to read from the input stream, to compute a
+        // FastLoad file checksum.  In that case, the implementation used
+        // nsIFastLoadFileIO to get the corresponding input stream for this
+        // output stream.
+        if (count == 0) {
+            gFastLoadService->SetOutputStream(nsnull);
+            rv = objectOutput->Close();
+
+            if (NS_SUCCEEDED(rv) && gChecksumXULFastLoadFile) {
+                rv = gFastLoadService->CacheChecksum(gFastLoadFile,
+                                                     objectOutput);
+            }
+        }
+    }
+
+    if (objectInput) {
+        // If this is the last of one or more XUL master documents loaded
+        // together at app startup, close the FastLoad service's singleton
+        // input stream now.
+        if (count == 0) {
+            gFastLoadService->SetInputStream(nsnull);
+            rv2 = objectInput->Close();
+        }
+    }
+
+    // If the list is empty now, the FastLoad process is done.
+    if (count == 0) {
+        NS_RELEASE(gFastLoadService);
+        NS_RELEASE(gFastLoadFile);
+    }
 
-    rv = aPrototypeDocument->Write(oos);
-    NS_ENSURE_SUCCESS(rv, rv);
-    FinishOutputStream(protoURI);
     return NS_FAILED(rv) ? rv : rv2;
 }
 
-nsresult
-nsXULPrototypeCache::GetInputStream(nsIURI* uri, nsIObjectInputStream** stream) 
-{
-    nsCAutoString spec;
-    uri->GetPath(spec);
-    
-    nsAutoArrayPtr<char> buf;
-    PRUint32 len;
-    nsCOMPtr<nsIObjectInputStream> ois;
-    if (!gStartupCache)
-        return NS_ERROR_NOT_AVAILABLE;
-    
-    nsresult rv = gStartupCache->GetBuffer(spec.get(), getter_Transfers(buf), 
-                                           &len);
-    if (NS_FAILED(rv)) 
-        return NS_ERROR_NOT_AVAILABLE;
-
-    rv = NS_NewObjectInputStreamFromBuffer(buf, len, getter_AddRefs(ois));
-    NS_ENSURE_SUCCESS(rv, rv);
-    buf.forget();
-
-    mInputStreamTable.Put(uri, ois);
-    
-    NS_ADDREF(*stream = ois);
-    return NS_OK;
-}
 
 nsresult
-nsXULPrototypeCache::FinishInputStream(nsIURI* uri) {
-    mInputStreamTable.Remove(uri);
-    return NS_OK;
-}
-
-nsresult
-nsXULPrototypeCache::GetOutputStream(nsIURI* uri, nsIObjectOutputStream** stream)
+nsXULPrototypeCache::StartFastLoadingURI(nsIURI* aURI, PRInt32 aDirectionFlags)
 {
     nsresult rv;
-    nsCOMPtr<nsIObjectOutputStream> objectOutput;
-    nsCOMPtr<nsIStorageStream> storageStream;
-    PRBool found = mOutputStreamTable.Get(uri, getter_AddRefs(storageStream));
-    if (found) {
-        objectOutput = do_CreateInstance("mozilla.org/binaryoutputstream;1");
-        if (!objectOutput) return NS_ERROR_OUT_OF_MEMORY;
-        nsCOMPtr<nsIOutputStream> outputStream
-            = do_QueryInterface(storageStream);
-        objectOutput->SetOutputStream(outputStream);
-    } else {
-        rv = NS_NewObjectOutputWrappedStorageStream(getter_AddRefs(objectOutput), 
-                                                    getter_AddRefs(storageStream),
-                                                    false);
-        NS_ENSURE_SUCCESS(rv, rv);
-        mOutputStreamTable.Put(uri, storageStream);
-    }
-    NS_ADDREF(*stream = objectOutput);
-    return NS_OK;
-}
 
-nsresult
-nsXULPrototypeCache::FinishOutputStream(nsIURI* uri) 
-{
-    nsresult rv;
-    if (!gStartupCache)
-        return NS_ERROR_NOT_AVAILABLE;
-    
-    nsCOMPtr<nsIStorageStream> storageStream;
-    PRBool found = mOutputStreamTable.Get(uri, getter_AddRefs(storageStream));
-    if (!found)
-        return NS_ERROR_UNEXPECTED;
-    nsCOMPtr<nsIOutputStream> outputStream
-        = do_QueryInterface(storageStream);
-    outputStream->Close();
-    
-    nsAutoArrayPtr<char> buf;
-    PRUint32 len;
-    rv = NS_NewBufferFromStorageStream(storageStream, getter_Transfers(buf), 
-                                       &len);
-    NS_ENSURE_SUCCESS(rv, rv);
+    nsCAutoString urlspec;
+    rv = aURI->GetAsciiSpec(urlspec);
+    if (NS_FAILED(rv)) return rv;
 
-    nsCAutoString spec;
-    uri->GetPath(spec);
-    rv = gStartupCache->PutBuffer(spec.get(), buf, len);
-    if (NS_SUCCEEDED(rv))
-        mOutputStreamTable.Remove(uri);
-    
-    return rv;
-}
-
-// We have data if we're in the middle of writing it or we already
-// have it in the cache.
-nsresult
-nsXULPrototypeCache::HasData(nsIURI* uri, PRBool* exists)
-{
-    if (mOutputStreamTable.Get(uri, nsnull)) {
-        *exists = PR_TRUE;
-        return NS_OK;
-    }
-    nsCAutoString spec;
-    uri->GetPath(spec);
-    nsAutoArrayPtr<char> buf;
-    PRUint32 len;
-    nsresult rv;
-    if (gStartupCache)
-        rv = gStartupCache->GetBuffer(spec.get(), getter_Transfers(buf), 
-                                      &len);
-    else {
-        // We don't have everything we need to call BeginCaching and set up
-        // gStartupCache right now, but we just need to check the cache for 
-        // this URI.
-        StartupCache* sc = StartupCache::GetSingleton();
-        if (!sc) {
-            *exists = PR_FALSE;
-            return NS_OK;
-        }
-        rv = sc->GetBuffer(spec.get(), getter_Transfers(buf), &len);
-    }
-    *exists = NS_SUCCEEDED(rv);
-    return NS_OK;
+    // If StartMuxedDocument returns NS_ERROR_NOT_AVAILABLE, then
+    // we must be reading the file, and urlspec was not associated
+    // with any multiplexed stream in it.  The FastLoad service
+    // will therefore arrange to update the file, writing new data
+    // at the end while old (available) data continues to be read
+    // from the pre-existing part of the file.
+    return gFastLoadService->StartMuxedDocument(aURI, urlspec.get(), aDirectionFlags);
 }
 
 static int
-CachePrefChangedCallback(const char* aPref, void* aClosure)
+FastLoadPrefChangedCallback(const char* aPref, void* aClosure)
 {
-    PRBool wasEnabled = !gDisableXULDiskCache;
-    gDisableXULDiskCache =
-        Preferences::GetBool(kDisableXULCachePref,
-                             gDisableXULDiskCache);
+    PRBool wasEnabled = !gDisableXULFastLoad;
+    gDisableXULFastLoad =
+        Preferences::GetBool(kDisableXULFastLoadPref, gDisableXULFastLoad);
 
-    if (wasEnabled && gDisableXULDiskCache) {
+    if (wasEnabled && gDisableXULFastLoad) {
         static NS_DEFINE_CID(kXULPrototypeCacheCID, NS_XULPROTOTYPECACHE_CID);
         nsCOMPtr<nsIXULPrototypeCache> cache =
             do_GetService(kXULPrototypeCacheCID);
 
         if (cache)
-            cache->AbortCaching();
+            cache->AbortFastLoads();
     }
+
+    gChecksumXULFastLoadFile =
+        Preferences::GetBool(kChecksumXULFastLoadFilePref,
+                             gChecksumXULFastLoadFile);
+
     return 0;
 }
 
+
+class nsXULFastLoadFileIO : public nsIFastLoadFileIO
+{
+  public:
+    nsXULFastLoadFileIO(nsIFile* aFile)
+      : mFile(aFile), mTruncateOutputFile(true) {
+    }
+
+    virtual ~nsXULFastLoadFileIO() {
+    }
+
+    NS_DECL_ISUPPORTS
+    NS_DECL_NSIFASTLOADFILEIO
+
+    nsCOMPtr<nsIFile>         mFile;
+    nsCOMPtr<nsIInputStream>  mInputStream;
+    nsCOMPtr<nsIOutputStream> mOutputStream;
+    bool mTruncateOutputFile;
+};
+
+
+NS_IMPL_THREADSAFE_ISUPPORTS1(nsXULFastLoadFileIO, nsIFastLoadFileIO)
+
+
+NS_IMETHODIMP
+nsXULFastLoadFileIO::GetInputStream(nsIInputStream** aResult)
+{
+    if (! mInputStream) {
+        nsresult rv;
+        nsCOMPtr<nsIInputStream> fileInput;
+        rv = NS_NewLocalFileInputStream(getter_AddRefs(fileInput), mFile);
+        if (NS_FAILED(rv)) return rv;
+
+        rv = NS_NewBufferedInputStream(getter_AddRefs(mInputStream),
+                                       fileInput,
+                                       XUL_DESERIALIZATION_BUFFER_SIZE);
+        if (NS_FAILED(rv)) return rv;
+    }
+
+    NS_ADDREF(*aResult = mInputStream);
+    return NS_OK;
+}
+
+
+NS_IMETHODIMP
+nsXULFastLoadFileIO::GetOutputStream(nsIOutputStream** aResult)
+{
+    if (! mOutputStream) {
+        PRInt32 ioFlags = PR_WRONLY;
+        if (mTruncateOutputFile)
+            ioFlags |= PR_CREATE_FILE | PR_TRUNCATE;
+
+        nsresult rv;
+        nsCOMPtr<nsIOutputStream> fileOutput;
+        rv = NS_NewLocalFileOutputStream(getter_AddRefs(fileOutput), mFile,
+                                         ioFlags, 0644);
+        if (NS_FAILED(rv)) return rv;
+
+        rv = NS_NewBufferedOutputStream(getter_AddRefs(mOutputStream),
+                                        fileOutput,
+                                        XUL_SERIALIZATION_BUFFER_SIZE);
+        if (NS_FAILED(rv)) return rv;
+    }
+
+    NS_ADDREF(*aResult = mOutputStream);
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsXULFastLoadFileIO::DisableTruncate()
+{
+    mTruncateOutputFile = false;
+    return NS_OK;
+}
+
 nsresult
-nsXULPrototypeCache::BeginCaching(nsIURI* aURI)
+nsXULPrototypeCache::StartFastLoad(nsIURI* aURI)
 {
     nsresult rv;
 
@@ -605,37 +703,47 @@ nsXULPrototypeCache::BeginCaching(nsIURI* aURI)
     if (!StringEndsWith(path, NS_LITERAL_CSTRING(".xul")))
         return NS_ERROR_NOT_AVAILABLE;
 
-    // Test gStartupCache to decide whether this is the first nsXULDocument
-    // participating in the serialization.  If gStartupCache is non-null, this document
-    // must not be first, but it can join the process.  Examples of
+    // Test gFastLoadFile to decide whether this is the first nsXULDocument
+    // participating in FastLoad.  If gFastLoadFile is non-null, this document
+    // must not be first, but it can join the FastLoad process.  Examples of
     // multiple master documents participating include hiddenWindow.xul and
     // navigator.xul on the Mac, and multiple-app-component (e.g., mailnews
     // and browser) startup due to command-line arguments.
     //
-    if (gStartupCache) {
-        mCacheURITable.Put(aURI, 1);
+    // XXXbe we should attempt to update the FastLoad file after startup!
+    //
+    // XXXbe we do not yet use nsFastLoadPtrs, but once we do, we must keep
+    // the FastLoad input stream open for the life of the app.
+    if (gFastLoadService && gFastLoadFile) {
+        mFastLoadURITable.Put(aURI, 1);
 
         return NS_OK;
     }
 
     // Use a local to refer to the service till we're sure we succeeded, then
-    // commit to gStartupCache.
-    StartupCache* startupCache = StartupCache::GetSingleton();
-    if (!startupCache)
+    // commit to gFastLoadService.  Same for gFastLoadFile, which is used to
+    // delete the FastLoad file on abort.
+    nsCOMPtr<nsIFastLoadService> fastLoadService(do_GetFastLoadService());
+    if (! fastLoadService)
         return NS_ERROR_FAILURE;
 
-    gDisableXULDiskCache =
-        Preferences::GetBool(kDisableXULCachePref, gDisableXULDiskCache);
-
-    nsContentUtils::RegisterPrefCallback(kDisableXULCachePref,
-                                         CachePrefChangedCallback,
+    gDisableXULFastLoad =
+        Preferences::GetBool(kDisableXULFastLoadPref, gDisableXULFastLoad);
+    gChecksumXULFastLoadFile =
+        Preferences::GetBool(kChecksumXULFastLoadFilePref,
+                             gChecksumXULFastLoadFile);
+    nsContentUtils::RegisterPrefCallback(kDisableXULFastLoadPref,
+                                         FastLoadPrefChangedCallback,
+                                         nsnull);
+    nsContentUtils::RegisterPrefCallback(kChecksumXULFastLoadFilePref,
+                                         FastLoadPrefChangedCallback,
                                          nsnull);
 
-    if (gDisableXULDiskCache)
+    if (gDisableXULFastLoad)
         return NS_ERROR_NOT_AVAILABLE;
 
     // Get the chrome directory to validate against the one stored in the
-    // cache file, or to store there if we're generating a new file.
+    // FastLoad file, or to store there if we're generating a new file.
     nsCOMPtr<nsIFile> chromeDir;
     rv = NS_GetSpecialDirectory(NS_APP_CHROME_DIR, getter_AddRefs(chromeDir));
     if (NS_FAILED(rv))
@@ -645,85 +753,134 @@ nsXULPrototypeCache::BeginCaching(nsIURI* aURI)
     if (NS_FAILED(rv))
         return rv;
 
+    nsCOMPtr<nsIFile> file;
+    rv = fastLoadService->NewFastLoadFile(XUL_FASTLOAD_FILE_BASENAME,
+                                          getter_AddRefs(file));
+    if (NS_FAILED(rv))
+        return rv;
+
+    // Give the FastLoad service an object by which it can get or create a
+    // file output stream given an input stream on the same file.
+    nsXULFastLoadFileIO* xio = new nsXULFastLoadFileIO(file);
+    nsCOMPtr<nsIFastLoadFileIO> io = static_cast<nsIFastLoadFileIO*>(xio);
+    if (! io)
+        return NS_ERROR_OUT_OF_MEMORY;
+    fastLoadService->SetFileIO(io);
+
+    nsCOMPtr<nsIXULChromeRegistry> chromeReg =
+        mozilla::services::GetXULChromeRegistryService();
+    if (!chromeReg)
+        return NS_ERROR_FAILURE;
+
     // XXXbe we assume the first package's locale is the same as the locale of
-    // all subsequent packages of cached chrome URIs....
+    // all subsequent packages of FastLoaded chrome URIs....
     nsCAutoString package;
     rv = aURI->GetHost(package);
     if (NS_FAILED(rv))
         return rv;
-    nsCOMPtr<nsIXULChromeRegistry> chromeReg
-        = do_GetService(NS_CHROMEREGISTRY_CONTRACTID, &rv);
+
     nsCAutoString locale;
     rv = chromeReg->GetSelectedLocale(package, locale);
     if (NS_FAILED(rv))
         return rv;
 
-    nsCAutoString fileChromePath, fileLocale;
-    
-    nsAutoArrayPtr<char> buf;
-    PRUint32 len, amtRead;
-    nsCOMPtr<nsIObjectInputStream> objectInput;
+    // Try to read an existent FastLoad file.
+    PRBool exists = PR_FALSE;
+    if (NS_SUCCEEDED(file->Exists(&exists)) && exists) {
+        nsCOMPtr<nsIObjectInputStream> objectInput;
+        rv = fastLoadService->NewInputStream(file, getter_AddRefs(objectInput));
 
-    rv = startupCache->GetBuffer(kXULCacheInfoKey, getter_Transfers(buf), 
-                                 &len);
-    if (NS_SUCCEEDED(rv))
-        rv = NS_NewObjectInputStreamFromBuffer(buf, len, getter_AddRefs(objectInput));
-    
-    if (NS_SUCCEEDED(rv)) {
-        buf.forget();
-        rv = objectInput->ReadCString(fileLocale);
-        rv |= objectInput->ReadCString(fileChromePath);
-        if (NS_FAILED(rv) ||
-            (!fileChromePath.Equals(chromePath) ||
-             !fileLocale.Equals(locale))) {
-            // Our cache won't be valid in this case, we'll need to rewrite.
-            // XXX This blows away work that other consumers (like
-            // mozJSComponentLoader) have done, need more fine-grained control.
-            startupCache->InvalidateCache();
-            rv = NS_ERROR_UNEXPECTED;
-        }
-    } else if (rv != NS_ERROR_NOT_AVAILABLE)
-        // NS_ERROR_NOT_AVAILABLE is normal, usually if there's no cachefile.
-        return rv;
+        if (NS_SUCCEEDED(rv)) {
+            if (NS_SUCCEEDED(rv)) {
+                // Get the XUL fastload file version number, which should be
+                // decremented whenever the XUL-specific file format changes
+                // (see public/nsIXULPrototypeCache.h for the #define).
+                PRUint32 xulFastLoadVersion, jsByteCodeVersion;
+                rv = objectInput->Read32(&xulFastLoadVersion);
+                rv |= objectInput->Read32(&jsByteCodeVersion);
+                if (NS_SUCCEEDED(rv)) {
+                    if (xulFastLoadVersion != XUL_FASTLOAD_FILE_VERSION ||
+                        jsByteCodeVersion != JSXDR_BYTECODE_VERSION) {
+#ifdef DEBUG
+                        printf((xulFastLoadVersion != XUL_FASTLOAD_FILE_VERSION)
+                               ? "bad FastLoad file version\n"
+                               : "bad JS bytecode version\n");
+#endif
+                        rv = NS_ERROR_UNEXPECTED;
+                    } else {
+                        nsCAutoString fileChromePath, fileLocale;
 
-    if (NS_FAILED(rv)) {
-        // Either the cache entry was invalid or it didn't exist, so write it now.
-        nsCOMPtr<nsIObjectOutputStream> objectOutput;
-        nsCOMPtr<nsIInputStream> inputStream;
-        nsCOMPtr<nsIStorageStream> storageStream;
-        rv = NS_NewObjectOutputWrappedStorageStream(getter_AddRefs(objectOutput),
-                                                    getter_AddRefs(storageStream),
-                                                    false);
-        if (NS_SUCCEEDED(rv)) {
-            rv = objectOutput->WriteStringZ(locale.get());
-            rv |= objectOutput->WriteStringZ(chromePath.get());
-            rv |= objectOutput->Close();
-            rv |= storageStream->NewInputStream(0, getter_AddRefs(inputStream));
-        }
-        if (NS_SUCCEEDED(rv))
-            rv = inputStream->Available(&len);
-        
-        if (NS_SUCCEEDED(rv)) {
-            buf = new char[len];
-            rv = inputStream->Read(buf, len, &amtRead);
-            if (NS_SUCCEEDED(rv) && len == amtRead)
-                rv = startupCache->PutBuffer(kXULCacheInfoKey, buf, len);
-            else {
-                rv = NS_ERROR_UNEXPECTED;
+                        rv = objectInput->ReadCString(fileChromePath);
+                        rv |= objectInput->ReadCString(fileLocale);
+                        if (NS_SUCCEEDED(rv) &&
+                            (!fileChromePath.Equals(chromePath) ||
+                             !fileLocale.Equals(locale))) {
+                            rv = NS_ERROR_UNEXPECTED;
+                        }
+                    }
+                }
             }
         }
 
-        // Failed again, just bail.
-        if (NS_FAILED(rv)) {
-            startupCache->InvalidateCache();
-            return NS_ERROR_FAILURE;
+        if (NS_SUCCEEDED(rv)) {
+            fastLoadService->SetInputStream(objectInput);
+        } else {
+            // NB: we must close before attempting to remove, for non-Unix OSes
+            // that can't do open-unlink.
+            if (objectInput)
+                objectInput->Close();
+            xio->mInputStream = nsnull;
+
+#ifdef DEBUG
+            file->MoveToNative(nsnull, NS_LITERAL_CSTRING("Invalid.mfasl"));
+#else
+            file->Remove(PR_FALSE);
+#endif
+            exists = PR_FALSE;
         }
     }
 
-    // Success!  Insert this URI into the mCacheURITable
-    // and commit locals to globals.
-    mCacheURITable.Put(aURI, 1);
+    // FastLoad file not found, or invalid: write a new one.
+    if (! exists) {
+        nsCOMPtr<nsIOutputStream> output;
+        rv = io->GetOutputStream(getter_AddRefs(output));
+        if (NS_FAILED(rv))
+            return rv;
 
-    gStartupCache = startupCache;
+        nsCOMPtr<nsIObjectOutputStream> objectOutput;
+        rv = fastLoadService->NewOutputStream(output,
+                                              getter_AddRefs(objectOutput));
+        if (NS_SUCCEEDED(rv)) {
+            rv = objectOutput->Write32(XUL_FASTLOAD_FILE_VERSION);
+            rv |= objectOutput->Write32(JSXDR_BYTECODE_VERSION);
+            rv |= objectOutput->WriteStringZ(chromePath.get());
+            rv |= objectOutput->WriteStringZ(locale.get());
+        }
+
+        // Remove here even though some errors above will lead to a FastLoad
+        // file invalidation.  Other errors (failure to note the dependency on
+        // installed-chrome.txt, e.g.) will not cause invalidation, and we may
+        // as well tidy up now.
+        if (NS_FAILED(rv)) {
+            if (objectOutput)
+                objectOutput->Close();
+            else
+                output->Close();
+            xio->mOutputStream = nsnull;
+
+            file->Remove(PR_FALSE);
+            return NS_ERROR_FAILURE;
+        }
+
+        fastLoadService->SetOutputStream(objectOutput);
+    }
+
+    // Success!  Insert this URI into the mFastLoadURITable
+    // and commit locals to globals.
+    mFastLoadURITable.Put(aURI, 1);
+
+    NS_ADDREF(gFastLoadService = fastLoadService);
+    NS_ADDREF(gFastLoadFile = file);
     return NS_OK;
 }
+
diff --git a/content/xul/document/src/nsXULPrototypeCache.h b/content/xul/document/src/nsXULPrototypeCache.h
index 38e1ff18321..a5ad3f37906 100644
--- a/content/xul/document/src/nsXULPrototypeCache.h
+++ b/content/xul/document/src/nsXULPrototypeCache.h
@@ -52,12 +52,8 @@
 #include "nsRefPtrHashtable.h"
 #include "nsURIHashKey.h"
 #include "nsXULPrototypeDocument.h"
-#include "nsIInputStream.h"
-#include "nsIStorageStream.h"
-#include "mozilla/scache/StartupCache.h"
-
-using namespace mozilla::scache;
 
+class nsIFastLoadService;
 class nsCSSStyleSheet;
 
 struct CacheScriptEntry
@@ -72,7 +68,7 @@ struct CacheScriptEntry
  *
  * The cache has two levels:
  *  1. In-memory hashtables
- *  2. The on-disk cache file.
+ *  2. The on-disk fastload file.
  */
 class nsXULPrototypeCache : public nsIXULPrototypeCache,
                                    nsIObserver
@@ -86,7 +82,7 @@ public:
     virtual PRBool IsCached(nsIURI* aURI) {
         return GetPrototype(aURI) != nsnull;
     }
-    virtual void AbortCaching();
+    virtual void AbortFastLoads();
 
 
     /**
@@ -100,6 +96,16 @@ public:
      */
     void Flush();
 
+    /**
+     * Remove a XUL document from the set of loading documents.
+     */
+    void RemoveFromFastLoadSet(nsIURI* aDocumentURI);
+
+    /**
+     * Write the XUL prototype document to fastload file. The proto must be
+     * fully loaded.
+     */
+    nsresult WritePrototype(nsXULPrototypeDocument* aPrototypeDocument);
 
     // The following methods are used to put and retrive various items into and
     // from the cache.
@@ -129,30 +135,9 @@ public:
      */
     nsresult PutStyleSheet(nsCSSStyleSheet* aStyleSheet);
 
-    /**
-     * Remove a XUL document from the set of loading documents.
-     */
-    void RemoveFromCacheSet(nsIURI* aDocumentURI);
-
-    /**
-     * Write the XUL prototype document to a cache file. The proto must be
-     * fully loaded.
-     */
-    nsresult WritePrototype(nsXULPrototypeDocument* aPrototypeDocument);
-
-    /**
-     * This interface allows partial reads and writes from the buffers in the
-     * startupCache.
-     */
-    nsresult GetInputStream(nsIURI* aURI, nsIObjectInputStream** objectInput);
-    nsresult FinishInputStream(nsIURI* aURI);
-    nsresult GetOutputStream(nsIURI* aURI, nsIObjectOutputStream** objectOutput);
-    nsresult FinishOutputStream(nsIURI* aURI);
-    nsresult HasData(nsIURI* aURI, PRBool* exists);
-
-    static StartupCache* GetStartupCache();
 
     static nsXULPrototypeCache* GetInstance();
+    static nsIFastLoadService* GetFastLoadService();
 
     static void ReleaseGlobals()
     {
@@ -177,16 +162,16 @@ protected:
     nsRefPtrHashtable<nsURIHashKey,nsXBLDocumentInfo>  mXBLDocTable;
 
     ///////////////////////////////////////////////////////////////////////////
-    // StartupCache
+    // FastLoad
     // this is really a hash set, with a dummy data parameter
-    nsDataHashtable<nsURIHashKey,PRUint32> mCacheURITable;
+    nsDataHashtable<nsURIHashKey,PRUint32> mFastLoadURITable;
 
-    static StartupCache* gStartupCache;
-    nsInterfaceHashtable<nsURIHashKey, nsIStorageStream> mOutputStreamTable;
-    nsInterfaceHashtable<nsURIHashKey, nsIObjectInputStream> mInputStreamTable;
- 
-    // Bootstrap caching service
-    nsresult BeginCaching(nsIURI* aDocumentURI);
+    static nsIFastLoadService*    gFastLoadService;
+    static nsIFile*               gFastLoadFile;
+
+    // Bootstrap FastLoad Service
+    nsresult StartFastLoad(nsIURI* aDocumentURI);
+    nsresult StartFastLoadingURI(nsIURI* aURI, PRInt32 aDirectionFlags);
 };
 
 #endif // nsXULPrototypeCache_h__
diff --git a/content/xul/document/src/nsXULPrototypeDocument.cpp b/content/xul/document/src/nsXULPrototypeDocument.cpp
index 775561ea34c..918592e3ea0 100644
--- a/content/xul/document/src/nsXULPrototypeDocument.cpp
+++ b/content/xul/document/src/nsXULPrototypeDocument.cpp
@@ -418,13 +418,6 @@ nsXULPrototypeDocument::Write(nsIObjectOutputStream* aStream)
     rv |= aStream->WriteObject(mNodeInfoManager->DocumentPrincipal(),
                                PR_TRUE);
     
-#ifdef DEBUG
-    // XXX Worrisome if we're caching things without system principal.
-    if (nsContentUtils::IsSystemPrincipal(mNodeInfoManager->DocumentPrincipal())) {
-        NS_WARNING("Serializing document without system principal");
-    }
-#endif
-
     // nsINodeInfo table
     nsCOMArray<nsINodeInfo> nodeInfos;
     if (mRoot)
diff --git a/js/src/xpconnect/loader/mozJSComponentLoader.cpp b/js/src/xpconnect/loader/mozJSComponentLoader.cpp
index 736e7352f81..d813d677359 100644
--- a/js/src/xpconnect/loader/mozJSComponentLoader.cpp
+++ b/js/src/xpconnect/loader/mozJSComponentLoader.cpp
@@ -969,8 +969,7 @@ mozJSComponentLoader::WriteScript(StartupCache* cache, JSObject *scriptObj,
     nsCOMPtr<nsIObjectOutputStream> oos;
     nsCOMPtr<nsIStorageStream> storageStream; 
     rv = NS_NewObjectOutputWrappedStorageStream(getter_AddRefs(oos),
-                                                getter_AddRefs(storageStream),
-                                                true);
+                                                getter_AddRefs(storageStream));
     NS_ENSURE_SUCCESS(rv, rv);
 
     rv = WriteScriptToStream(cx, scriptObj, oos);
diff --git a/startupcache/StartupCacheUtils.cpp b/startupcache/StartupCacheUtils.cpp
index 6a7a6313f0d..538b2517154 100644
--- a/startupcache/StartupCacheUtils.cpp
+++ b/startupcache/StartupCacheUtils.cpp
@@ -27,8 +27,7 @@ NS_NewObjectInputStreamFromBuffer(char* buffer, PRUint32 len,
 
 NS_EXPORT nsresult
 NS_NewObjectOutputWrappedStorageStream(nsIObjectOutputStream **wrapperStream,
-                                       nsIStorageStream** stream,
-				       PRBool wantDebugStream)
+                                       nsIStorageStream** stream)
 {
   nsCOMPtr<nsIStorageStream> storageStream;
 
@@ -43,17 +42,13 @@ NS_NewObjectOutputWrappedStorageStream(nsIObjectOutputStream **wrapperStream,
   objectOutput->SetOutputStream(outputStream);
   
 #ifdef DEBUG
-  if (wantDebugStream) {
-    // Wrap in debug stream to detect unsupported writes of 
-    // multiply-referenced non-singleton objects
-    StartupCache* sc = StartupCache::GetSingleton();
-    NS_ENSURE_TRUE(sc, NS_ERROR_UNEXPECTED);
-    nsCOMPtr<nsIObjectOutputStream> debugStream;
-    sc->GetDebugObjectOutputStream(objectOutput, getter_AddRefs(debugStream));
-    debugStream.forget(wrapperStream);
-  } else {
-    objectOutput.forget(wrapperStream);
-  }
+  // Wrap in debug stream to detect unsupported writes of 
+  // multiply-referenced non-singleton objects
+  StartupCache* sc = StartupCache::GetSingleton();
+  NS_ENSURE_TRUE(sc, NS_ERROR_UNEXPECTED);
+  nsCOMPtr<nsIObjectOutputStream> debugStream;
+  sc->GetDebugObjectOutputStream(objectOutput, getter_AddRefs(debugStream));
+  debugStream.forget(wrapperStream);
 #else
   objectOutput.forget(wrapperStream);
 #endif
diff --git a/startupcache/StartupCacheUtils.h b/startupcache/StartupCacheUtils.h
index 7828ba224af..05021b12d51 100644
--- a/startupcache/StartupCacheUtils.h
+++ b/startupcache/StartupCacheUtils.h
@@ -50,15 +50,10 @@ NS_NewObjectInputStreamFromBuffer(char* buffer, PRUint32 len,
                                   nsIObjectInputStream** stream);
 
 // We can't retrieve the wrapped stream from the objectOutputStream later,
-// so we return it here. We give callers in debug builds the option 
-// to wrap the outputstream in a debug stream, which will detect if
-// non-singleton objects are written out multiple times during a serialization.
-// This could cause them to be deserialized incorrectly (as multiple copies
-// instead of references).
+// so we return it here.
 NS_EXPORT nsresult
 NS_NewObjectOutputWrappedStorageStream(nsIObjectOutputStream **wrapperStream,
-                                       nsIStorageStream** stream,
-                                       PRBool wantDebugStream);
+                                       nsIStorageStream** stream);
 
 NS_EXPORT nsresult
 NS_NewBufferFromStorageStream(nsIStorageStream *storageStream, 
diff --git a/startupcache/nsStartupCacheUtils.cpp b/startupcache/nsStartupCacheUtils.cpp
new file mode 100644
index 00000000000..bcc9cab24e3
--- /dev/null
+++ b/startupcache/nsStartupCacheUtils.cpp
@@ -0,0 +1,124 @@
+/* -*-  Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is Startup Cache.
+ *
+ * The Initial Developer of the Original Code is
+ * The Mozilla Foundation <http://www.mozilla.org/>.
+ * Portions created by the Initial Developer are Copyright (C) 2009
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *  Benedict Hsieh <bhsieh@mozilla.com>
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+#include "nsStartupCacheUtils.h"
+
+#include "nsCOMPtr.h"
+#include "nsComponentManagerUtils.h"
+#include "nsIInputStream.h"
+#include "nsIStorageStream.h"
+#include "nsIStringStream.h"
+#include "nsIObjectInputStream.h"
+#include "nsIObjectOutputStream.h"
+
+nsresult
+NS_NewObjectInputStreamFromBuffer(char* buffer, int len, 
+                                  nsIObjectInputStream** stream)
+{
+  nsCOMPtr<nsIStringInputStream> stringStream
+    = do_CreateInstance("@mozilla.org/io/string-input-stream;1");
+  if (!stringStream)
+    return NS_ERROR_OUT_OF_MEMORY;
+  nsCOMPtr<nsIObjectInputStream> objectInput 
+    = do_CreateInstance("@mozilla.org/binaryinputstream;1");
+  if (!objectInput)
+    return NS_ERROR_OUT_OF_MEMORY;
+
+  stringStream->AdoptData(buffer, len);
+  objectInput->SetInputStream(stringStream);
+
+  NS_ADDREF(*stream = objectInput);
+  return NS_OK;
+}
+
+// This is questionable API name and design, but we can't
+// retrieve the wrapped stream from the objectOutputStream later...
+nsresult
+NS_NewObjectOutputWrappedStorageStream(nsIObjectOutputStream **wrapperStream,
+                                       nsIStorageStream** stream)
+{
+  nsCOMPtr<nsIStorageStream> storageStream;
+  nsresult rv = NS_NewStorageStream(256, (PRUint32)-1, 
+                                    getter_AddRefs(storageStream));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIObjectOutputStream> objectOutput
+    = do_CreateInstance("@mozilla.org/binaryoutputstream;1");
+  if (!objectOutput)
+    return NS_ERROR_OUT_OF_MEMORY;
+
+  nsCOMPtr<nsIOutputStream> outputStream
+    = do_QueryInterface(storageStream);
+
+  objectOutput->SetOutputStream(outputStream);
+  NS_ADDREF(*wrapperStream = objectOutput);
+  NS_ADDREF(*stream = storageStream);
+  return NS_OK;
+}
+
+nsresult
+NS_NewBufferFromStorageStream(nsIStorageStream *storageStream, 
+                              char** buffer, int* len)
+{
+  nsresult rv;
+  nsCOMPtr<nsIInputStream> inputStream;
+  rv = storageStream->NewInputStream(0, getter_AddRefs(inputStream));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  PRUint32 avail, read;
+  rv = inputStream->Available(&avail);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  char* temp = new char[avail];
+  if (!temp)
+    return NS_ERROR_OUT_OF_MEMORY;
+
+  rv = inputStream->Read(temp, avail, &read);
+  if (NS_SUCCEEDED(rv) && avail != read)
+    rv = NS_ERROR_UNEXPECTED;
+
+  if (NS_FAILED(rv)) {
+    delete temp;
+    return rv;
+  }
+
+  *len = avail;
+  *buffer = temp;
+  return NS_OK;
+}
+