diff --git a/b2g/app/b2g.js b/b2g/app/b2g.js
index 0149d3bf411b..ab7fe85df438 100644
--- a/b2g/app/b2g.js
+++ b/b2g/app/b2g.js
@@ -1021,9 +1021,7 @@ pref("identity.fxaccounts.remote.profile.uri", "https://profile.accounts.firefox
 pref("identity.fxaccounts.skipDeviceRegistration", true);
 
 // Enable mapped array buffer.
-#ifndef XP_WIN
 pref("dom.mapped_arraybuffer.enabled", true);
-#endif
 
 // SystemUpdate API
 pref("dom.system_update.enabled", true);
diff --git a/dom/base/test/chrome.ini b/dom/base/test/chrome.ini
index 576a25cea24d..e88449f57981 100644
--- a/dom/base/test/chrome.ini
+++ b/dom/base/test/chrome.ini
@@ -20,8 +20,6 @@ subsuite = clipboard
 [test_messagemanager_send_principal.html]
 skip-if = buildapp == 'mulet'
 [test_bug945152.html]
-run-if = os == 'linux'
 [test_bug1008126.html]
-run-if = os == 'linux'
 [test_sandboxed_blob_uri.html]
 [test_websocket_frame.html]
diff --git a/dom/xhr/XMLHttpRequestMainThread.cpp b/dom/xhr/XMLHttpRequestMainThread.cpp
index fe6b6f6b90f4..2420306b91db 100644
--- a/dom/xhr/XMLHttpRequestMainThread.cpp
+++ b/dom/xhr/XMLHttpRequestMainThread.cpp
@@ -2728,7 +2728,7 @@ XMLHttpRequestMainThread::Send(nsIVariant* aVariant, const Nullable<RequestBody>
 
   mIsMappedArrayBuffer = false;
   if (mResponseType == XMLHttpRequestResponseType::Arraybuffer &&
-      Preferences::GetBool("dom.mapped_arraybuffer.enabled", false)) {
+      Preferences::GetBool("dom.mapped_arraybuffer.enabled", true)) {
     nsCOMPtr<nsIURI> uri;
     nsAutoCString scheme;
 
@@ -3757,11 +3757,6 @@ nsresult
 ArrayBufferBuilder::mapToFileInPackage(const nsCString& aFile,
                                        nsIFile* aJarFile)
 {
-#ifdef XP_WIN
-  // TODO: Bug 988813 - Support memory mapped array buffer for Windows platform.
-  MOZ_CRASH("Not implemented");
-  return NS_ERROR_NOT_IMPLEMENTED;
-#else
   nsresult rv;
 
   // Open Jar file to get related attributes of target file.
@@ -3793,7 +3788,6 @@ ArrayBufferBuilder::mapToFileInPackage(const nsCString& aFile,
     }
   }
   return NS_ERROR_FAILURE;
-#endif
 }
 
 /* static */ bool
diff --git a/js/src/gc/Memory.cpp b/js/src/gc/Memory.cpp
index 735e1080e2f8..e4024b6f26fa 100644
--- a/js/src/gc/Memory.cpp
+++ b/js/src/gc/Memory.cpp
@@ -280,6 +280,61 @@ GetPageFaultCount()
     return pmc.PageFaultCount;
 }
 
+// On Windows the minimum size for a mapping is the allocation granularity
+// (64KiB in practice), so mapping very small buffers is potentially wasteful.
+void*
+AllocateMappedContent(int fd, size_t offset, size_t length, size_t alignment)
+{
+    // The allocation granularity must be a whole multiple of the alignment and
+    // the caller must request an aligned offset to satisfy Windows' and the
+    // caller's alignment requirements.
+    if (allocGranularity % alignment != 0 || offset % alignment != 0)
+        return nullptr;
+
+    // Make sure file exists and do sanity check for offset and size.
+    HANDLE hFile = reinterpret_cast<HANDLE>(intptr_t(fd));
+    MOZ_ASSERT(hFile != INVALID_HANDLE_VALUE);
+
+    uint32_t fSizeHgh;
+    uint32_t fSizeLow = GetFileSize(hFile, LPDWORD(&fSizeHgh));
+    if (fSizeLow == INVALID_FILE_SIZE && GetLastError() != NO_ERROR)
+        return nullptr;
+
+    uint64_t fSize = (uint64_t(fSizeHgh) << 32) + fSizeLow;
+    if (offset >= size_t(fSize) || length == 0 || length > fSize - offset)
+        return nullptr;
+
+    uint64_t mapSize = length + offset;
+    HANDLE hMap = CreateFileMapping(hFile, nullptr, PAGE_READONLY, mapSize >> 32, mapSize, nullptr);
+    if (!hMap)
+        return nullptr;
+
+    // MapViewOfFile requires the offset to be a whole multiple of the
+    // allocation granularity.
+    size_t alignOffset = offset - (offset % allocGranularity);
+    size_t alignLength = length + (offset % allocGranularity);
+    void* map = MapViewOfFile(hMap, FILE_MAP_COPY, 0, alignOffset, alignLength);
+    CloseHandle(hMap);
+    if (!map)
+        return nullptr;
+
+    return reinterpret_cast<void*>(uintptr_t(map) + (offset - alignOffset));
+}
+
+void
+DeallocateMappedContent(void* p, size_t /*length*/)
+{
+    if (!p)
+        return;
+
+    // Calculate the address originally returned by MapViewOfFile.
+    // This is required because AllocateMappedContent returns a pointer that
+    // might be offset into the view, necessitated by the requirement that the
+    // beginning of a view must be aligned with the allocation granularity.
+    uintptr_t map = uintptr_t(p) - (uintptr_t(p) % allocGranularity);
+    MOZ_ALWAYS_TRUE(UnmapViewOfFile(reinterpret_cast<void*>(map)));
+}
+
 #  else // Various APIs are unavailable.
 
 void*
@@ -328,12 +383,10 @@ GetPageFaultCount()
     return 0;
 }
 
-#  endif
-
 void*
 AllocateMappedContent(int fd, size_t offset, size_t length, size_t alignment)
 {
-    // TODO: Bug 988813 - Support memory mapped array buffer for Windows platform.
+    // Not implemented.
     return nullptr;
 }
 
@@ -341,9 +394,11 @@ AllocateMappedContent(int fd, size_t offset, size_t length, size_t alignment)
 void
 DeallocateMappedContent(void* p, size_t length)
 {
-    // TODO: Bug 988813 - Support memory mapped array buffer for Windows platform.
+    // Not implemented.
 }
 
+#  endif
+
 #elif defined(SOLARIS)
 
 #ifndef MAP_NOSYNC
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index a172036e25b5..7bfbb247cdad 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -5053,8 +5053,8 @@ pref("dom.voicemail.enabled", false);
 // parameter omitted.
 pref("dom.voicemail.defaultServiceId", 0);
 
-// Disable mapped array buffer by default.
-pref("dom.mapped_arraybuffer.enabled", false);
+// Enable mapped array buffer by default.
+pref("dom.mapped_arraybuffer.enabled", true);
 
 // The tables used for Safebrowsing phishing and malware checks.
 pref("urlclassifier.malwareTable", "goog-malware-shavar,goog-unwanted-shavar,test-malware-simple,test-unwanted-simple");