diff --git a/modules/libjar/nsZipArchive.cpp b/modules/libjar/nsZipArchive.cpp
index a25cfadb19a..2310cf29c86 100644
--- a/modules/libjar/nsZipArchive.cpp
+++ b/modules/libjar/nsZipArchive.cpp
@@ -30,6 +30,7 @@
 #define ZIP_ARENABLOCKSIZE (1*1024)
 
 #ifdef XP_UNIX
+    #include <sys/mman.h>
     #include <sys/types.h>
     #include <sys/stat.h>
     #include <limits.h>
@@ -156,6 +157,9 @@ nsresult gZlibInit(z_stream *zs)
 nsZipHandle::nsZipHandle()
   : mFileData(nullptr)
   , mLen(0)
+#if defined(XP_WIN)
+  , mFd(nullptr)
+#endif
   , mMap(nullptr)
   , mRefCnt(0)
 {
@@ -168,7 +172,11 @@ NS_IMPL_THREADSAFE_RELEASE(nsZipHandle)
 nsresult nsZipHandle::Init(nsIFile *file, nsZipHandle **ret)
 {
   mozilla::AutoFDClose fd;
-  nsresult rv = file->OpenNSPRFileDesc(PR_RDONLY, 0000, &fd.rwget());
+  int32_t flags = PR_RDONLY;
+#if defined(XP_WIN)
+  flags |= nsIFile::OS_READAHEAD;
+#endif
+  nsresult rv = file->OpenNSPRFileDesc(flags, 0000, &fd.rwget());
   if (NS_FAILED(rv))
     return rv;
 
@@ -194,6 +202,9 @@ nsresult nsZipHandle::Init(nsIFile *file, nsZipHandle **ret)
     return NS_ERROR_OUT_OF_MEMORY;
   }
 
+#if defined(XP_WIN)
+  handle->mFd = fd.forget();
+#endif
   handle->mMap = map;
   handle->mFile.Init(file);
   handle->mLen = (uint32_t) size;
@@ -231,6 +242,11 @@ int64_t nsZipHandle::SizeOfMapping()
 
 nsZipHandle::~nsZipHandle()
 {
+#if defined(XP_WIN)
+  if (mFd) {
+    PR_Close(mFd);
+  }
+#endif
   if (mMap) {
     PR_MemUnmap((void *)mFileData, mLen);
     PR_CloseFileMap(mMap);
@@ -569,6 +585,15 @@ MOZ_WIN_MEM_TRY_BEGIN
   uint32_t centralOffset = 4;
   if (mFd->mLen > ZIPCENTRAL_SIZE && xtolong(startp + centralOffset) == CENTRALSIG) {
     // Success means optimized jar layout from bug 559961 is in effect
+    uint32_t readaheadLength = xtolong(startp);
+    if (readaheadLength) {
+#if defined(XP_UNIX)
+      madvise(const_cast<uint8_t*>(startp), readaheadLength, MADV_WILLNEED);
+#elif defined(XP_WIN)
+      HANDLE hFile = (HANDLE) PR_FileDesc2NativeHandle(mFd->mFd);
+      mozilla::ReadAhead(hFile, 0, readaheadLength);
+#endif
+    }
   } else {
     for (buf = endp - ZIPEND_SIZE; buf > startp; buf--)
       {
diff --git a/modules/libjar/nsZipArchive.h b/modules/libjar/nsZipArchive.h
index 895a19ebd1d..ecb11ebc71b 100644
--- a/modules/libjar/nsZipArchive.h
+++ b/modules/libjar/nsZipArchive.h
@@ -392,6 +392,9 @@ private:
   nsZipHandle();
   ~nsZipHandle();
 
+#if defined(XP_WIN)
+  PRFileDesc *                      mFd;     /* nspr file descriptor */
+#endif
   PRFileMap *                       mMap;    /* nspr datastructure for mmap */
   nsAutoPtr<nsZipItemPtr<uint8_t> > mBuf;
   nsrefcnt                          mRefCnt; /* ref count */