diff --git a/dom/base/Navigator.cpp b/dom/base/Navigator.cpp
index a507dea841..0f7f2b756e 100644
--- a/dom/base/Navigator.cpp
+++ b/dom/base/Navigator.cpp
@@ -678,6 +678,18 @@ Navigator::CpuHasSSE2()
   return mozilla::supports_sse2();
 }
 
+bool
+Navigator::CpuHasAVX()
+{
+  return mozilla::supports_avx();
+}
+
+bool
+Navigator::CpuHasAVX2()
+{
+  return mozilla::supports_avx2();
+}
+
 void
 Navigator::RefreshMIMEArray()
 {
diff --git a/dom/base/Navigator.h b/dom/base/Navigator.h
index 69626d1a7c..10f9573ee9 100644
--- a/dom/base/Navigator.h
+++ b/dom/base/Navigator.h
@@ -173,6 +173,8 @@ public:
   bool JavaEnabled(ErrorResult& aRv);
   uint64_t HardwareConcurrency();
   bool CpuHasSSE2();
+  bool CpuHasAVX();
+  bool CpuHasAVX2();
   bool TaintEnabled()
   {
     return false;
diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index ce025a42f5..6fba48e48b 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -3550,6 +3550,8 @@ nsGlobalWindow::GetEventTargetParent(EventChainPreVisitor& aVisitor)
 
   aVisitor.mCanHandle = true;
   // Middle/right click shouldn't dispatch click event, use auxclick to instead.
+  // Note: mDoc should always exist here, but check just in case someone yanked
+  // it out from under us.
   if (mDoc && mDoc->IsXULDocument()) {
     aVisitor.mForceContentDispatch = true; //FIXME! Bug 329119
   }
diff --git a/dom/webidl/Navigator.webidl b/dom/webidl/Navigator.webidl
index 60ed84d535..f2212de392 100644
--- a/dom/webidl/Navigator.webidl
+++ b/dom/webidl/Navigator.webidl
@@ -211,6 +211,10 @@ partial interface Navigator {
    */
   [ChromeOnly]
   readonly attribute boolean cpuHasSSE2;
+  [ChromeOnly]
+  readonly attribute boolean cpuHasAVX;
+  [ChromeOnly]
+  readonly attribute boolean cpuHasAVX2;
 };
 
 // nsIDOMNavigatorDesktopNotification
diff --git a/gfx/thebes/D3D11Checks.cpp b/gfx/thebes/D3D11Checks.cpp
index b5be58ff53..9619884472 100644
--- a/gfx/thebes/D3D11Checks.cpp
+++ b/gfx/thebes/D3D11Checks.cpp
@@ -246,7 +246,11 @@ DoesTextureSharingWorkInternal(ID3D11Device *device, DXGI_FORMAT format, UINT bi
   }
 
   RefPtr<IDXGIKeyedMutex> sourceSharedMutex;
-  texture->QueryInterface(__uuidof(IDXGIKeyedMutex), (void**)getter_AddRefs(sourceSharedMutex));
+  HRESULT hr = texture->QueryInterface(__uuidof(IDXGIKeyedMutex), (void**)getter_AddRefs(sourceSharedMutex));
+  if (FAILED(hr) || !sourceSharedMutex) {
+    gfxCriticalNote << "Failed to acquire IDXGIKeyedMutex; texture sharing disabled.";
+    return false;
+  }
   if (FAILED(sourceSharedMutex->AcquireSync(0, 30*1000))) {
     gfxCriticalError() << "DoesD3D11TextureSharingWork_SourceMutexTimeout";
     // only wait for 30 seconds
@@ -306,9 +310,12 @@ DoesTextureSharingWorkInternal(ID3D11Device *device, DXGI_FORMAT format, UINT bi
   }
 
   RefPtr<IDXGIKeyedMutex> sharedMutex;
-  sharedResource->QueryInterface(__uuidof(IDXGIKeyedMutex), (void**)getter_AddRefs(sharedMutex));
-  {
-    HRESULT hr;
+  hr = sharedResource->QueryInterface(__uuidof(IDXGIKeyedMutex), (void**)getter_AddRefs(sharedMutex));
+  if (FAILED(hr) || !sharedMutex) {
+    gfxCriticalNote << "Failed to acquire IDXGIKeyedMutex; texture sharing disabled.";
+    return false;
+  }
+  { // Scope for mutex lock.
     AutoTextureLock lock(sharedMutex, hr, 30*1000);
     if (FAILED(hr)) {
       gfxCriticalError() << "DoesD3D11TextureSharingWork_AcquireSyncTimeout";
diff --git a/toolkit/content/aboutSupport.js b/toolkit/content/aboutSupport.js
index 9f4ee08a2e..b14bcba63f 100644
--- a/toolkit/content/aboutSupport.js
+++ b/toolkit/content/aboutSupport.js
@@ -39,6 +39,10 @@ var snapshotFormatters = {
     $("application-box").textContent = data.name;
     $("useragent-box").textContent = data.userAgent;
     $("os-box").textContent = data.osVersion;
+    let cpucaps = navigator.cpuHasSSE2?"SSE2 ":"";
+    cpucaps    += navigator.cpuHasAVX?"AVX ":"";
+    cpucaps    += navigator.cpuHasAVX2?"AVX2 ":"";
+    $("cpucap-box").textContent = cpucaps;
     $("binary-box").textContent = Services.dirsvc.get("XREExeF", Ci.nsIFile).path;
     $("supportLink").href = data.supportURL;
     let version = Services.appinfo.version;
diff --git a/toolkit/content/aboutSupport.xhtml b/toolkit/content/aboutSupport.xhtml
index 9a2425e2bf..839ee8eb55 100644
--- a/toolkit/content/aboutSupport.xhtml
+++ b/toolkit/content/aboutSupport.xhtml
@@ -142,6 +142,15 @@
             </td>
           </tr>
 
+          <tr>
+            <th class="column">
+              &aboutSupport.appBasicsCPUCaps;
+            </th>
+
+            <td id="cpucap-box">
+            </td>
+          </tr>
+
           <tr class="no-copy">
             <th class="column">
               &aboutSupport.appBasicsBinary;
diff --git a/toolkit/locales/en-US/chrome/global/aboutSupport.dtd b/toolkit/locales/en-US/chrome/global/aboutSupport.dtd
index f827268b43..96d9deef0d 100644
--- a/toolkit/locales/en-US/chrome/global/aboutSupport.dtd
+++ b/toolkit/locales/en-US/chrome/global/aboutSupport.dtd
@@ -47,6 +47,7 @@ Windows/Mac use the term "Folder" instead of "Directory" -->
 <!ENTITY aboutSupport.appBasicsBuildConfig "Build Configuration">
 <!ENTITY aboutSupport.appBasicsUserAgent "User Agent">
 <!ENTITY aboutSupport.appBasicsOS "OS">
+<!ENTITY aboutSupport.appBasicsCPUCaps "CPU Capabilities">
 <!ENTITY aboutSupport.appBasicsMemoryUse "Memory Use">
 <!ENTITY aboutSupport.appBasicsPerformance "Performance">
 
diff --git a/toolkit/modules/UpdateUtils.jsm b/toolkit/modules/UpdateUtils.jsm
index 5acf395d3d..31a9e933e0 100644
--- a/toolkit/modules/UpdateUtils.jsm
+++ b/toolkit/modules/UpdateUtils.jsm
@@ -66,6 +66,7 @@ this.UpdateUtils = {
     let custom = prefBranch.getCharPref(PREF_APP_UPDATE_CUSTOM, "");
     let distribution = prefBranch.getCharPref(PREF_APP_DISTRIBUTION, "default");
     let distributionVersion = prefBranch.getCharPref(PREF_APP_DISTRIBUTION_VERSION, "default");
+    let navigator = Services.appShell.hiddenDOMWindow.navigator;
 
     let substs = [
       [/%ID%/g,                     Services.appinfo.ID],
@@ -81,7 +82,10 @@ this.UpdateUtils = {
       [/%PLATFORM_VERSION%/g,       Services.appinfo.platformVersion],
       [/%DISTRIBUTION%/g,           distribution],
       [/%DISTRIBUTION_VERSION%/g,   distributionVersion],
-      [/%LOCALE%/g,                 this.Locale]     
+      [/%LOCALE%/g,                 this.Locale],
+      [/%CPU_SSE2%/g,               navigator.cpuHasSSE2],
+      [/%CPU_AVX%/g,                navigator.cpuHasAVX],
+      [/%CPU_AVX2%/g,               navigator.cpuHasAVX2]
     ];
 
     substs.forEach(([_subst, _value]) => aUpdateURL = aUpdateURL.replace(_subst, _value));