diff --git a/dom/base/nsDOMException.cpp b/dom/base/nsDOMException.cpp
index 8782eab0dcf..4a70382b42d 100644
--- a/dom/base/nsDOMException.cpp
+++ b/dom/base/nsDOMException.cpp
@@ -177,7 +177,7 @@ NSResultToNameAndMessage(nsresult aNSResult,
 
 nsresult
 NS_GetNameAndMessageForDOMNSResult(nsresult aNSResult, const char** aName,
-                                   const char** aMessage)
+                                   const char** aMessage, PRUint16* aCode)
 {
   const char* name = nsnull;
   const char* message = nsnull;
@@ -187,6 +187,9 @@ NS_GetNameAndMessageForDOMNSResult(nsresult aNSResult, const char** aName,
   if (name && message) {
     *aName = name;
     *aMessage = message;
+    if (aCode) {
+      *aCode = code;
+    }
     return NS_OK;
   }
 
diff --git a/dom/base/nsDOMException.h b/dom/base/nsDOMException.h
index 677925d254e..57a0c6f8d20 100644
--- a/dom/base/nsDOMException.h
+++ b/dom/base/nsDOMException.h
@@ -64,7 +64,8 @@ protected:
 
 nsresult
 NS_GetNameAndMessageForDOMNSResult(nsresult aNSResult, const char** aName,
-                                   const char** aMessage);
+                                   const char** aMessage,
+                                   PRUint16* aCode = nsnull);
 
 #define DECL_INTERNAL_DOM_EXCEPTION(domname)                                 \
 nsresult                                                                     \
diff --git a/dom/bindings/Utils.h b/dom/bindings/Utils.h
index f2db75b0cad..e5b4be1f0d7 100644
--- a/dom/bindings/Utils.h
+++ b/dom/bindings/Utils.h
@@ -8,6 +8,7 @@
 #define mozilla_dom_bindings_Utils_h__
 
 #include "mozilla/dom/bindings/DOMJSClass.h"
+#include "mozilla/dom/workers/Workers.h"
 
 #include "jsapi.h"
 #include "jsfriendapi.h"
@@ -25,12 +26,14 @@ template<bool mainThread>
 inline bool
 Throw(JSContext* cx, nsresult rv)
 {
+  using mozilla::dom::workers::exceptions::ThrowDOMExceptionForNSResult;
+
   // XXX Introduce exception machinery.
   if (mainThread) {
     XPCThrower::Throw(rv, cx);
   } else {
     if (!JS_IsExceptionPending(cx)) {
-      JS_ReportError(cx, "Exception thrown (nsresult = %x).", rv);
+      ThrowDOMExceptionForNSResult(cx, rv);
     }
   }
   return false;
diff --git a/dom/workers/Exceptions.cpp b/dom/workers/Exceptions.cpp
index 70d78b4e0de..f7103e70943 100644
--- a/dom/workers/Exceptions.cpp
+++ b/dom/workers/Exceptions.cpp
@@ -43,6 +43,7 @@
 #include "jsfriendapi.h"
 #include "jsprf.h"
 #include "mozilla/Util.h"
+#include "nsDOMException.h"
 #include "nsTraceRefcnt.h"
 
 #include "WorkerInlines.h"
@@ -68,6 +69,7 @@ class DOMException : public PrivatizableBase
   enum SLOT {
     SLOT_code = 0,
     SLOT_name,
+    SLOT_message,
 
     SLOT_COUNT
   };
@@ -87,7 +89,7 @@ public:
   }
 
   static JSObject*
-  Create(JSContext* aCx, int aCode);
+  Create(JSContext* aCx, nsresult aNSResult);
 
 private:
   DOMException()
@@ -131,18 +133,23 @@ private:
       return false;
     }
 
-    char buf[100];
-    JS_snprintf(buf, sizeof(buf), "%s: ", sClass.name);
+    jsval name = JS_GetReservedSlot(obj, SLOT_name);
+    JS_ASSERT(name.isString());
 
-    JSString* classString = JS_NewStringCopyZ(aCx, buf);
-    if (!classString) {
+    JSString *colon = JS_NewStringCopyN(aCx, ": ", 2);
+    if (!colon){
       return false;
     }
 
-    jsval name = JS_GetReservedSlot(obj, SLOT_name);
-    JS_ASSERT(JSVAL_IS_STRING(name));
+    JSString* out = JS_ConcatStrings(aCx, name.toString(), colon);
+    if (!out) {
+      return false;
+    }
 
-    JSString* out = JS_ConcatStrings(aCx, classString, JSVAL_TO_STRING(name));
+    jsval message = JS_GetReservedSlot(obj, SLOT_message);
+    JS_ASSERT(message.isString());
+
+    out = JS_ConcatStrings(aCx, out, message.toString());
     if (!out) {
       return false;
     }
@@ -190,6 +197,7 @@ JSClass DOMException::sClass = {
 JSPropertySpec DOMException::sProperties[] = {
   { "code", SLOT_code, PROPERTY_FLAGS, GetProperty, js_GetterOnlyPropertyStub },
   { "name", SLOT_name, PROPERTY_FLAGS, GetProperty, js_GetterOnlyPropertyStub },
+  { "message", SLOT_message, PROPERTY_FLAGS, GetProperty, js_GetterOnlyPropertyStub },
   { 0, 0, 0, NULL, NULL }
 };
 
@@ -203,9 +211,6 @@ JSPropertySpec DOMException::sStaticProperties[] = {
 #define EXCEPTION_ENTRY(_name) \
   { #_name, _name, CONSTANT_FLAGS, GetConstant, NULL },
 
-  // Make sure this one is always first.
-  EXCEPTION_ENTRY(UNKNOWN_ERR)
-
   EXCEPTION_ENTRY(INDEX_SIZE_ERR)
   EXCEPTION_ENTRY(DOMSTRING_SIZE_ERR)
   EXCEPTION_ENTRY(HIERARCHY_REQUEST_ERR)
@@ -239,32 +244,35 @@ JSPropertySpec DOMException::sStaticProperties[] = {
 
 // static
 JSObject*
-DOMException::Create(JSContext* aCx, int aCode)
+DOMException::Create(JSContext* aCx, nsresult aNSResult)
 {
   JSObject* obj = JS_NewObject(aCx, &sClass, NULL, NULL);
   if (!obj) {
     return NULL;
   }
 
-  size_t foundIndex = size_t(-1);
-  for (size_t index = 0; index < ArrayLength(sStaticProperties) - 1; index++) {
-    if (sStaticProperties[index].tinyid == aCode) {
-      foundIndex = index;
-      break;
-    }
-  }
-
-  if (foundIndex == size_t(-1)) {
-    foundIndex = 0;
-  }
-
-  JSString* name = JS_NewStringCopyZ(aCx, sStaticProperties[foundIndex].name);
-  if (!name) {
+  const char* name;
+  const char* message;
+  uint16_t code;
+  if (NS_FAILED(NS_GetNameAndMessageForDOMNSResult(aNSResult, &name, &message,
+                                                   &code))) {
+    JS_ReportError(aCx, "Exception thrown (nsresult = 0x%x).", aNSResult);
     return NULL;
   }
 
-  JS_SetReservedSlot(obj, SLOT_code, INT_TO_JSVAL(aCode));
-  JS_SetReservedSlot(obj, SLOT_name, STRING_TO_JSVAL(name));
+  JSString* jsname = JS_NewStringCopyZ(aCx, name);
+  if (!jsname) {
+    return NULL;
+  }
+
+  JSString* jsmessage = JS_NewStringCopyZ(aCx, message);
+  if (!jsmessage) {
+    return NULL;
+  }
+
+  JS_SetReservedSlot(obj, SLOT_code, INT_TO_JSVAL(code));
+  JS_SetReservedSlot(obj, SLOT_name, STRING_TO_JSVAL(jsname));
+  JS_SetReservedSlot(obj, SLOT_message, STRING_TO_JSVAL(jsmessage));
 
   DOMException* priv = new DOMException();
   SetJSPrivateSafeish(obj, priv);
@@ -272,147 +280,6 @@ DOMException::Create(JSContext* aCx, int aCode)
   return obj;
 }
 
-class FileException : public PrivatizableBase
-{
-  static JSClass sClass;
-  static JSPropertySpec sProperties[];
-  static JSPropertySpec sStaticProperties[];
-
-  enum SLOT {
-    SLOT_code = 0,
-    SLOT_name,
-
-    SLOT_COUNT
-  };
-
-public:
-  static JSObject*
-  InitClass(JSContext* aCx, JSObject* aObj)
-  {
-    return JS_InitClass(aCx, aObj, NULL, &sClass, Construct, 0, sProperties,
-                        NULL, sStaticProperties, NULL);
-  }
-
-  static JSObject*
-  Create(JSContext* aCx, int aCode);
-
-private:
-  FileException()
-  {
-    MOZ_COUNT_CTOR(mozilla::dom::workers::exceptions::FileException);
-  }
-
-  ~FileException()
-  {
-    MOZ_COUNT_DTOR(mozilla::dom::workers::exceptions::FileException);
-  }
-
-  static JSBool
-  Construct(JSContext* aCx, unsigned aArgc, jsval* aVp)
-  {
-    JS_ReportErrorNumber(aCx, js_GetErrorMessage, NULL, JSMSG_WRONG_CONSTRUCTOR,
-                         sClass.name);
-    return false;
-  }
-
-  static void
-  Finalize(JSFreeOp* aFop, JSObject* aObj)
-  {
-    JS_ASSERT(JS_GetClass(aObj) == &sClass);
-    delete GetJSPrivateSafeish<FileException>(aObj);
-  }
-
-  static JSBool
-  GetProperty(JSContext* aCx, JSObject* aObj, jsid aIdval, jsval* aVp)
-  {
-    JS_ASSERT(JSID_IS_INT(aIdval));
-
-    int32 slot = JSID_TO_INT(aIdval);
-
-    JSClass* classPtr = JS_GetClass(aObj);
-
-    if (classPtr != &sClass || !GetJSPrivateSafeish<FileException>(aObj)) {
-      JS_ReportErrorNumber(aCx, js_GetErrorMessage, NULL,
-                           JSMSG_INCOMPATIBLE_PROTO, sClass.name,
-                           sProperties[slot].name, classPtr->name);
-      return false;
-    }
-
-    *aVp = JS_GetReservedSlot(aObj, slot);
-    return true;
-  }
-
-  static JSBool
-  GetConstant(JSContext* aCx, JSObject* aObj, jsid idval, jsval* aVp)
-  {
-    JS_ASSERT(JSID_IS_INT(idval));
-    *aVp = INT_TO_JSVAL(JSID_TO_INT(idval));
-    return true;
-  }
-};
-
-JSClass FileException::sClass = {
-  "FileException",
-  JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(SLOT_COUNT),
-  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
-  JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, Finalize
-};
-
-JSPropertySpec FileException::sProperties[] = {
-  { "code", SLOT_code, PROPERTY_FLAGS, GetProperty, js_GetterOnlyPropertyStub },
-  { "name", SLOT_name, PROPERTY_FLAGS, GetProperty, js_GetterOnlyPropertyStub },
-  { 0, 0, 0, NULL, NULL }
-};
-
-JSPropertySpec FileException::sStaticProperties[] = {
-
-#define EXCEPTION_ENTRY(_name) \
-  { #_name, FILE_##_name, CONSTANT_FLAGS, GetConstant, NULL },
-
-  EXCEPTION_ENTRY(NOT_FOUND_ERR)
-  EXCEPTION_ENTRY(SECURITY_ERR)
-  EXCEPTION_ENTRY(ABORT_ERR)
-  EXCEPTION_ENTRY(NOT_READABLE_ERR)
-  EXCEPTION_ENTRY(ENCODING_ERR)
-
-#undef EXCEPTION_ENTRY
-
-  { 0, 0, 0, NULL, NULL }
-};
-
-// static
-JSObject*
-FileException::Create(JSContext* aCx, int aCode)
-{
-  JSObject* obj = JS_NewObject(aCx, &sClass, NULL, NULL);
-  if (!obj) {
-    return NULL;
-  }
-
-  size_t foundIndex = size_t(-1);
-  for (size_t index = 0; index < ArrayLength(sStaticProperties) - 1; index++) {
-    if (sStaticProperties[index].tinyid == aCode) {
-      foundIndex = index;
-      break;
-    }
-  }
-
-  JS_ASSERT(foundIndex != size_t(-1));
-
-  JSString* name = JS_NewStringCopyZ(aCx, sStaticProperties[foundIndex].name);
-  if (!name) {
-    return NULL;
-  }
-
-  JS_SetReservedSlot(obj, SLOT_code, INT_TO_JSVAL(aCode));
-  JS_SetReservedSlot(obj, SLOT_name, STRING_TO_JSVAL(name));
-
-  FileException* priv = new FileException();
-  SetJSPrivateSafeish(obj, priv);
-
-  return obj;
-}
-
 } // anonymous namespace
 
 BEGIN_WORKERS_NAMESPACE
@@ -422,24 +289,16 @@ namespace exceptions {
 bool
 InitClasses(JSContext* aCx, JSObject* aGlobal)
 {
-  return DOMException::InitClass(aCx, aGlobal) &&
-         FileException::InitClass(aCx, aGlobal);
+  return DOMException::InitClass(aCx, aGlobal);
 }
 
 void
-ThrowDOMExceptionForCode(JSContext* aCx, int aCode)
+ThrowDOMExceptionForNSResult(JSContext* aCx, nsresult aNSResult)
 {
-  JSObject* exception = DOMException::Create(aCx, aCode);
-  JS_ASSERT(exception);
-
-  JS_SetPendingException(aCx, OBJECT_TO_JSVAL(exception));
-}
-
-void
-ThrowFileExceptionForCode(JSContext* aCx, int aCode)
-{
-  JSObject* exception = FileException::Create(aCx, aCode);
-  JS_ASSERT(exception);
+  JSObject* exception = DOMException::Create(aCx, aNSResult);
+  if (!exception) {
+    return;
+  }
 
   JS_SetPendingException(aCx, OBJECT_TO_JSVAL(exception));
 }
diff --git a/dom/workers/Exceptions.h b/dom/workers/Exceptions.h
index c83608c8b83..75839816d73 100644
--- a/dom/workers/Exceptions.h
+++ b/dom/workers/Exceptions.h
@@ -71,16 +71,6 @@
 #define INVALID_NODE_TYPE_ERR 24
 #define DATA_CLONE_ERR 25
 
-// This one isn't actually spec'd anywhere, use it when we can't find a match.
-#define UNKNOWN_ERR 0
-
-// FileException Codes
-#define FILE_NOT_FOUND_ERR 1
-#define FILE_SECURITY_ERR 2
-#define FILE_ABORT_ERR 3
-#define FILE_NOT_READABLE_ERR 4
-#define FILE_ENCODING_ERR 5
-
 BEGIN_WORKERS_NAMESPACE
 
 namespace exceptions {
@@ -88,12 +78,6 @@ namespace exceptions {
 bool
 InitClasses(JSContext* aCx, JSObject* aGlobal);
 
-void
-ThrowDOMExceptionForCode(JSContext* aCx, int aCode);
-
-void
-ThrowFileExceptionForCode(JSContext* aCx, int aCode);
-
 } // namespace exceptions
 
 END_WORKERS_NAMESPACE
diff --git a/dom/workers/File.cpp b/dom/workers/File.cpp
index 96a96911ac0..b895863072b 100644
--- a/dom/workers/File.cpp
+++ b/dom/workers/File.cpp
@@ -41,6 +41,7 @@
 
 #include "nsIDOMFile.h"
 #include "nsDOMBlobBuilder.h"
+#include "nsDOMError.h"
 
 #include "jsapi.h"
 #include "jsatom.h"
@@ -58,8 +59,7 @@
 
 USING_WORKERS_NAMESPACE
 
-using mozilla::dom::workers::exceptions::ThrowDOMExceptionForCode;
-using mozilla::dom::workers::exceptions::ThrowFileExceptionForCode;
+using mozilla::dom::workers::exceptions::ThrowDOMExceptionForNSResult;
 
 namespace {
 
@@ -125,9 +125,7 @@ private:
     nsresult rv = file->InitInternal(aCx, aArgc, JS_ARGV(aCx, aVp),
                                      Unwrap);
     if (NS_FAILED(rv)) {
-      ThrowDOMExceptionForCode(aCx,
-        NS_ERROR_GET_MODULE(rv) == NS_ERROR_MODULE_DOM ?
-          NS_ERROR_GET_CODE(rv) : UNKNOWN_ERR);
+      ThrowDOMExceptionForNSResult(aCx, rv);
       return false;
     }
 
@@ -159,7 +157,8 @@ private:
 
     PRUint64 size;
     if (NS_FAILED(blob->GetSize(&size))) {
-      ThrowFileExceptionForCode(aCx, FILE_NOT_READABLE_ERR);
+      ThrowDOMExceptionForNSResult(aCx, NS_ERROR_DOM_FILE_NOT_READABLE_ERR);
+      return false;
     }
 
     if (!JS_NewNumberValue(aCx, double(size), aVp)) {
@@ -179,7 +178,8 @@ private:
 
     nsString type;
     if (NS_FAILED(blob->GetType(type))) {
-      ThrowFileExceptionForCode(aCx, FILE_NOT_READABLE_ERR);
+      ThrowDOMExceptionForNSResult(aCx, NS_ERROR_DOM_FILE_NOT_READABLE_ERR);
+      return false;
     }
 
     JSString* jsType = JS_NewUCStringCopyN(aCx, type.get(), type.Length());
@@ -223,7 +223,7 @@ private:
                               static_cast<PRUint64>(end),
                               contentType, optionalArgc,
                               getter_AddRefs(rtnBlob)))) {
-      ThrowFileExceptionForCode(aCx, FILE_NOT_READABLE_ERR);
+      ThrowDOMExceptionForNSResult(aCx, NS_ERROR_DOM_FILE_NOT_READABLE_ERR);
       return false;
     }
 
@@ -350,7 +350,7 @@ private:
 
     if (GetWorkerPrivateFromContext(aCx)->UsesSystemPrincipal() &&
         NS_FAILED(file->GetMozFullPathInternal(fullPath))) {
-      ThrowFileExceptionForCode(aCx, FILE_NOT_READABLE_ERR);
+      ThrowDOMExceptionForNSResult(aCx, NS_ERROR_DOM_FILE_NOT_READABLE_ERR);
       return false;
     }
 
diff --git a/dom/workers/FileReaderSync.cpp b/dom/workers/FileReaderSync.cpp
index fc19d9f6ee6..55c3485f8c4 100644
--- a/dom/workers/FileReaderSync.cpp
+++ b/dom/workers/FileReaderSync.cpp
@@ -40,6 +40,7 @@
 #include "FileReaderSync.h"
 
 #include "nsIDOMFile.h"
+#include "nsDOMError.h"
 
 #include "jsapi.h"
 #include "jsatom.h"
@@ -56,7 +57,7 @@
 
 USING_WORKERS_NAMESPACE
 
-using mozilla::dom::workers::exceptions::ThrowFileExceptionForCode;
+using mozilla::dom::workers::exceptions::ThrowDOMExceptionForNSResult;
 
 namespace {
 
@@ -67,10 +68,10 @@ EnsureSucceededOrThrow(JSContext* aCx, nsresult rv)
     return true;
   }
 
-  int code = rv == NS_ERROR_FILE_NOT_FOUND ?
-              FILE_NOT_FOUND_ERR :
-              FILE_NOT_READABLE_ERR;
-  ThrowFileExceptionForCode(aCx, code);
+  rv = rv == NS_ERROR_FILE_NOT_FOUND ?
+              NS_ERROR_DOM_FILE_NOT_FOUND_ERR :
+              NS_ERROR_DOM_FILE_NOT_READABLE_ERR;
+  ThrowDOMExceptionForNSResult(aCx, rv);
   return false;
 }
 
diff --git a/dom/workers/WorkerPrivate.cpp b/dom/workers/WorkerPrivate.cpp
index a1390d5b608..22e2608bab3 100644
--- a/dom/workers/WorkerPrivate.cpp
+++ b/dom/workers/WorkerPrivate.cpp
@@ -100,7 +100,7 @@
 using mozilla::MutexAutoLock;
 using mozilla::TimeDuration;
 using mozilla::TimeStamp;
-using mozilla::dom::workers::exceptions::ThrowDOMExceptionForCode;
+using mozilla::dom::workers::exceptions::ThrowDOMExceptionForNSResult;
 
 USING_WORKERS_NAMESPACE
 using namespace mozilla::dom::workers::events;
@@ -415,7 +415,7 @@ struct WorkerStructuredCloneCallbacks
   static void
   Error(JSContext* aCx, uint32_t /* aErrorId */)
   {
-    ThrowDOMExceptionForCode(aCx, DATA_CLONE_ERR);
+    ThrowDOMExceptionForNSResult(aCx, NS_ERROR_DOM_DATA_CLONE_ERR);
   }
 };
 
diff --git a/dom/workers/Workers.h b/dom/workers/Workers.h
index 2f3aff8c91d..947a3541c1d 100644
--- a/dom/workers/Workers.h
+++ b/dom/workers/Workers.h
@@ -97,6 +97,14 @@ GetWorkerCrossThreadDispatcher(JSContext* aCx, jsval aWorker);
 // Random unique constant to facilitate JSPrincipal debugging
 const uint32_t kJSPrincipalsDebugToken = 0x7e2df9d2;
 
+namespace exceptions {
+
+// Implemented in Exceptions.cpp
+void
+ThrowDOMExceptionForNSResult(JSContext* aCx, nsresult aNSResult);
+
+} // namespace exceptions
+
 END_WORKERS_NAMESPACE
 
 #endif // mozilla_dom_workers_workers_h__
diff --git a/dom/workers/XMLHttpRequest.cpp b/dom/workers/XMLHttpRequest.cpp
index 58fd37bbd3a..8a4018275d0 100644
--- a/dom/workers/XMLHttpRequest.cpp
+++ b/dom/workers/XMLHttpRequest.cpp
@@ -34,7 +34,7 @@ USING_WORKERS_NAMESPACE
 namespace XMLHttpRequestResponseTypeValues = 
   mozilla::dom::bindings::prototypes::XMLHttpRequestResponseType;
 
-using mozilla::dom::workers::exceptions::ThrowDOMExceptionForCode;
+using mozilla::dom::workers::exceptions::ThrowDOMExceptionForNSResult;
 
 // XXX Need to figure this out...
 #define UNCATCHABLE_EXCEPTION NS_ERROR_OUT_OF_MEMORY
@@ -214,21 +214,6 @@ END_WORKERS_NAMESPACE
 
 namespace {
 
-inline int
-GetDOMExceptionCodeFromResult(nsresult aResult)
-{
-  if (NS_SUCCEEDED(aResult)) {
-    return 0;
-  }
-
-  if (NS_ERROR_GET_MODULE(aResult) == NS_ERROR_MODULE_DOM) {
-    return NS_ERROR_GET_CODE(aResult);
-  }
-
-  NS_WARNING("Update main thread implementation for a DOM error code here!");
-  return INVALID_STATE_ERR;
-}
-
 inline void
 ConvertResponseTypeToString(XMLHttpRequestResponseType aType, nsString& aString)
 {
@@ -783,11 +768,11 @@ private:
   class ResponseRunnable : public MainThreadProxyRunnable
   {
     PRUint32 mSyncQueueKey;
-    int mErrorCode;
+    nsresult mErrorCode;
 
   public:
     ResponseRunnable(WorkerPrivate* aWorkerPrivate, Proxy* aProxy,
-                     PRUint32 aSyncQueueKey, int aErrorCode)
+                     PRUint32 aSyncQueueKey, nsresult aErrorCode)
     : MainThreadProxyRunnable(aWorkerPrivate, SkipWhenClearing, aProxy),
       mSyncQueueKey(aSyncQueueKey), mErrorCode(aErrorCode)
     {
@@ -797,8 +782,8 @@ private:
     bool
     WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate)
     {
-      if (mErrorCode) {
-        ThrowDOMExceptionForCode(aCx, mErrorCode);
+      if (NS_FAILED(mErrorCode)) {
+        ThrowDOMExceptionForNSResult(aCx, mErrorCode);
         aWorkerPrivate->StopSyncLoop(mSyncQueueKey, false);
       }
       else {
@@ -836,7 +821,7 @@ public:
     return true;
   }
 
-  virtual int
+  virtual nsresult
   MainThreadRun() = 0;
 
   NS_IMETHOD
@@ -847,7 +832,7 @@ public:
     PRUint32 oldSyncQueueKey = mProxy->mSyncEventResponseSyncQueueKey;
     mProxy->mSyncEventResponseSyncQueueKey = mSyncQueueKey;
 
-    int rv = MainThreadRun();
+    nsresult rv = MainThreadRun();
 
     nsRefPtr<ResponseRunnable> response =
       new ResponseRunnable(mWorkerPrivate, mProxy, mSyncQueueKey, rv);
@@ -871,7 +856,7 @@ public:
     MOZ_ASSERT(aProxy);
   }
 
-  virtual int
+  virtual nsresult
   MainThreadRun()
   {
     AssertIsOnMainThread();
@@ -892,10 +877,10 @@ public:
   : WorkerThreadProxySyncRunnable(aWorkerPrivate, aProxy), mValue(aValue)
   { }
 
-  int
+  nsresult
   MainThreadRun()
   {
-    return GetDOMExceptionCodeFromResult(mProxy->mXHR->SetMultipart(mValue));
+    return mProxy->mXHR->SetMultipart(mValue);
   }
 };
 
@@ -909,11 +894,10 @@ public:
   : WorkerThreadProxySyncRunnable(aWorkerPrivate, aProxy), mValue(aValue)
   { }
 
-  int
+  nsresult
   MainThreadRun()
   {
-    nsresult rv = mProxy->mXHR->SetMozBackgroundRequest(mValue);
-    return GetDOMExceptionCodeFromResult(rv);
+    return mProxy->mXHR->SetMozBackgroundRequest(mValue);
   }
 };
 
@@ -927,11 +911,10 @@ public:
   : WorkerThreadProxySyncRunnable(aWorkerPrivate, aProxy), mValue(aValue)
   { }
 
-  int
+  nsresult
   MainThreadRun()
   {
-    nsresult rv = mProxy->mXHR->SetWithCredentials(mValue);
-    return GetDOMExceptionCodeFromResult(rv);
+    return mProxy->mXHR->SetWithCredentials(mValue);
   }
 };
 
@@ -946,7 +929,7 @@ public:
     mResponseType(aResponseType)
   { }
 
-  int
+  nsresult
   MainThreadRun()
   {
     nsresult rv = mProxy->mXHR->SetResponseType(mResponseType);
@@ -954,7 +937,7 @@ public:
     if (NS_SUCCEEDED(rv)) {
       rv = mProxy->mXHR->GetResponseType(mResponseType);
     }
-    return GetDOMExceptionCodeFromResult(rv);
+    return rv;
   }
 
   void
@@ -974,10 +957,10 @@ public:
     mTimeout(aTimeout)
   { }
 
-  int
+  nsresult
   MainThreadRun()
   {
-    return GetDOMExceptionCodeFromResult(mProxy->mXHR->SetTimeout(mTimeout));
+    return mProxy->mXHR->SetTimeout(mTimeout);
   }
 };
 
@@ -988,7 +971,7 @@ public:
   : WorkerThreadProxySyncRunnable(aWorkerPrivate, aProxy)
   { }
 
-  int
+  nsresult
   MainThreadRun()
   {
     mProxy->mInnerEventStreamId++;
@@ -1002,7 +985,7 @@ public:
 
     mProxy->Reset();
 
-    return 0;
+    return NS_OK;
   }
 };
 
@@ -1017,11 +1000,11 @@ public:
     mResponseHeaders(aResponseHeaders)
   { }
 
-  int
+  nsresult
   MainThreadRun()
   {
     mProxy->mXHR->GetAllResponseHeaders(mResponseHeaders);
-    return 0;
+    return NS_OK;
   }
 };
 
@@ -1037,11 +1020,10 @@ public:
     mValue(aValue)
   { }
 
-  int
+  nsresult
   MainThreadRun()
   {
-    nsresult rv = mProxy->mXHR->GetResponseHeader(mHeader, mValue);
-    return GetDOMExceptionCodeFromResult(rv);
+    return mProxy->mXHR->GetResponseHeader(mHeader, mValue);
   }
 };
 
@@ -1068,53 +1050,45 @@ public:
     mTimeout(aTimeout)
   { }
 
-  int
+  nsresult
   MainThreadRun()
   {
     WorkerPrivate* oldWorker = mProxy->mWorkerPrivate;
     mProxy->mWorkerPrivate = mWorkerPrivate;
 
-    int retval = MainThreadRunInternal();
+    nsresult rv = MainThreadRunInternal();
 
     mProxy->mWorkerPrivate = oldWorker;
-    return retval;
+    return rv;
   }
 
-  int
+  nsresult
   MainThreadRunInternal()
   {
     if (!mProxy->Init()) {
-      return INVALID_STATE_ERR;
+      return NS_ERROR_DOM_INVALID_STATE_ERR;
     }
 
     nsresult rv;
 
     if (mMultipart) {
       rv = mProxy->mXHR->SetMultipart(mMultipart);
-      if (NS_FAILED(rv)) {
-        return GetDOMExceptionCodeFromResult(rv);
-      }
+      NS_ENSURE_SUCCESS(rv, rv);
     }
 
     if (mBackgroundRequest) {
       rv = mProxy->mXHR->SetMozBackgroundRequest(mBackgroundRequest);
-      if (NS_FAILED(rv)) {
-        return GetDOMExceptionCodeFromResult(rv);
-      }
+      NS_ENSURE_SUCCESS(rv, rv);
     }
 
     if (mWithCredentials) {
       rv = mProxy->mXHR->SetWithCredentials(mWithCredentials);
-      if (NS_FAILED(rv)) {
-        return GetDOMExceptionCodeFromResult(rv);
-      }
+      NS_ENSURE_SUCCESS(rv, rv);
     }
 
     if (mTimeout) {
       rv = mProxy->mXHR->SetTimeout(mTimeout);
-      if (NS_FAILED(rv)) {
-        return GetDOMExceptionCodeFromResult(rv);
-      }
+      NS_ENSURE_SUCCESS(rv, rv);
     }
 
     NS_ASSERTION(!mProxy->mInOpen, "Reentrancy is bad!");
@@ -1129,7 +1103,7 @@ public:
       rv = mProxy->mXHR->SetResponseType(NS_LITERAL_STRING("text"));
     }
 
-    return GetDOMExceptionCodeFromResult(rv);
+    return rv;
   }
 };
 
@@ -1154,7 +1128,7 @@ public:
     mClonedObjects.SwapElements(aClonedObjects);
   }
 
-  int
+  nsresult
   MainThreadRun()
   {
     nsCOMPtr<nsIVariant> variant;
@@ -1164,7 +1138,7 @@ public:
       nsIXPConnect* xpc = nsContentUtils::XPConnect();
       NS_ASSERTION(xpc, "This should never be null!");
 
-      int error = 0;
+      nsresult rv = NS_OK;
 
       JSStructuredCloneCallbacks* callbacks =
         mWorkerPrivate->IsChromeWorker() ?
@@ -1175,24 +1149,22 @@ public:
       if (mBody.read(cx, &body, callbacks, &mClonedObjects)) {
         if (NS_FAILED(xpc->JSValToVariant(cx, &body,
                                           getter_AddRefs(variant)))) {
-          error = INVALID_STATE_ERR;
+          rv = NS_ERROR_DOM_INVALID_STATE_ERR;
         }
       }
       else {
-        error = DATA_CLONE_ERR;
+        rv = NS_ERROR_DOM_DATA_CLONE_ERR;
       }
 
       mBody.clear();
       mClonedObjects.Clear();
 
-      if (error) {
-        return error;
-      }
+      NS_ENSURE_SUCCESS(rv, rv);
     }
     else {
       nsCOMPtr<nsIWritableVariant> wvariant =
         do_CreateInstance(NS_VARIANT_CONTRACTID);
-      NS_ENSURE_TRUE(wvariant, UNKNOWN_ERR);
+      NS_ENSURE_TRUE(wvariant, NS_ERROR_UNEXPECTED);
 
       if (NS_FAILED(wvariant->SetAsAString(mStringBody))) {
         NS_ERROR("This should never fail!");
@@ -1229,7 +1201,7 @@ public:
       }
     }
 
-    return GetDOMExceptionCodeFromResult(rv);
+    return rv;
   }
 };
 
@@ -1245,11 +1217,10 @@ public:
     mValue(aValue)
   { }
 
-  int
+  nsresult
   MainThreadRun()
   {
-    nsresult rv = mProxy->mXHR->SetRequestHeader(mHeader, mValue);
-    return GetDOMExceptionCodeFromResult(rv);
+    return mProxy->mXHR->SetRequestHeader(mHeader, mValue);
   }
 };
 
@@ -1263,11 +1234,11 @@ public:
   : WorkerThreadProxySyncRunnable(aWorkerPrivate, aProxy), mMimeType(aMimeType)
   { }
 
-  int
+  nsresult
   MainThreadRun()
   {
     mProxy->mXHR->OverrideMimeType(mMimeType);
-    return 0;
+    return NS_OK;
   }
 };
 
diff --git a/dom/workers/test/xhr2_worker.js b/dom/workers/test/xhr2_worker.js
index 1d9e0ed5a83..18924a15a4e 100644
--- a/dom/workers/test/xhr2_worker.js
+++ b/dom/workers/test/xhr2_worker.js
@@ -66,6 +66,16 @@ onmessage = function(event) {
       throw new Error("Failed to throw when getting responseText on '" + type +
                       "' type");
     }
+
+    if (exception.name != "InvalidStateError") {
+      throw new Error("Unexpected error when getting responseText on '" + type +
+                      "' type");
+    }
+
+    if (exception.code != DOMException.INVALID_STATE_ERR) {
+      throw new Error("Unexpected error code when getting responseText on '" + type +
+                      "' type");
+    }
   }
 
   testResponseTextException("arraybuffer");
@@ -102,6 +112,16 @@ onmessage = function(event) {
                     "calling open()");
   }
 
+  if (exception.name != "InvalidStateError") {
+    throw new Error("Unexpected error when setting responseType before " +
+                    "calling open()");
+  }
+
+  if (exception.code != DOMException.INVALID_STATE_ERR) {
+    throw new Error("Unexpected error code when setting responseType before " +
+                    "calling open()");
+  }
+
   xhr.open("GET", url);
   xhr.responseType = "text";
   xhr.onload = function(event) {
@@ -152,4 +172,14 @@ onmessage = function(event) {
     throw new Error("Failed to throw when setting responseType after " +
                     "calling send()");
   }
+
+  if (exception.name != "InvalidStateError") {
+    throw new Error("Unexpected error when setting responseType after " +
+                    "calling send()");
+  }
+
+  if (exception.code != DOMException.INVALID_STATE_ERR) {
+    throw new Error("Unexpected error code when setting responseType after " +
+                    "calling send()");
+  }
 }