--- a/gfx/layers/apz/src/AsyncPanZoomController.cpp
+++ b/gfx/layers/apz/src/AsyncPanZoomController.cpp
@@ -3556,31 +3556,31 @@ ScrollableLayerGuid AsyncPanZoomControll
 
 void AsyncPanZoomController::UpdateSharedCompositorFrameMetrics()
 {
   mMonitor.AssertCurrentThreadIn();
 
   FrameMetrics* frame = mSharedFrameMetricsBuffer ?
       static_cast<FrameMetrics*>(mSharedFrameMetricsBuffer->memory()) : nullptr;
 
-  if (frame && mSharedLock && gfxPlatform::GetPlatform()->UseProgressivePaint()) {
+  if (frame && mSharedLock && gfxPlatform::GetPlatform()->SupportsCrossProcessMutex()) {
     mSharedLock->Lock();
     *frame = mFrameMetrics.MakePODObject();
     mSharedLock->Unlock();
   }
 }
 
 void AsyncPanZoomController::ShareCompositorFrameMetrics() {
 
   PCompositorParent* compositor = GetSharedFrameMetricsCompositor();
 
   // Only create the shared memory buffer if it hasn't already been created,
   // we are using progressive tile painting, and we have a
   // compositor to pass the shared memory back to the content process/thread.
-  if (!mSharedFrameMetricsBuffer && compositor && gfxPlatform::GetPlatform()->UseProgressivePaint()) {
+  if (!mSharedFrameMetricsBuffer && compositor && gfxPlatform::GetPlatform()->SupportsCrossProcessMutex()) {
 
     // Create shared memory and initialize it with the current FrameMetrics value
     mSharedFrameMetricsBuffer = new ipc::SharedMemoryBasic;
     FrameMetrics* frame = nullptr;
     mSharedFrameMetricsBuffer->Create(sizeof(FrameMetrics));
     mSharedFrameMetricsBuffer->Map(sizeof(FrameMetrics));
     frame = static_cast<FrameMetrics*>(mSharedFrameMetricsBuffer->memory());
 

--- a/gfx/thebes/gfxPlatform.cpp
+++ b/gfx/thebes/gfxPlatform.cpp
@@ -2179,17 +2179,18 @@ gfxPlatform::AsyncPanZoomEnabled()
 #else
   return gfxPrefs::AsyncPanZoomEnabledDoNotUseDirectly();
 #endif
 }
 
 /*virtual*/ bool
 gfxPlatform::UseProgressivePaint()
 {
-  return gfxPrefs::ProgressivePaintDoNotUseDirectly();
+  return SupportsCrossProcessMutex() &&
+    gfxPrefs::ProgressivePaintDoNotUseDirectly();
 }
 
 /*static*/ bool
 gfxPlatform::PerfWarnings()
 {
   return gfxPrefs::PerfWarnings();
 }
 

--- a/gfx/thebes/gfxPlatform.h
+++ b/gfx/thebes/gfxPlatform.h
@@ -241,30 +241,32 @@ public:
      * will return false.
      */
     bool SupportsAzureContentForDrawTarget(mozilla::gfx::DrawTarget* aTarget);
 
     bool SupportsAzureContentForType(mozilla::gfx::BackendType aType) {
       return BackendTypeBit(aType) & mContentBackendBitmask;
     }
 
+    virtual bool SupportsCrossProcessMutex() { return true; }
+
     /// This function lets us know if the current preferences/platform
     /// combination allows for both accelerated and not accelerated canvas
     /// implementations.  If it does, and other relevant preferences are
     /// asking for it, we will examine the commands in the first few seconds
     /// of the canvas usage, and potentially change to accelerated or
     /// non-accelerated canvas.
     virtual bool HaveChoiceOfHWAndSWCanvas();
 
     virtual bool UseAcceleratedSkiaCanvas();
     virtual void InitializeSkiaCacheLimits();
 
     /// These should be used instead of directly accessing the preference,
     /// as different platforms may override the behaviour.
-    virtual bool UseProgressivePaint();
+    bool UseProgressivePaint();
 
     static bool AsyncPanZoomEnabled();
 
     virtual void GetAzureBackendInfo(mozilla::widget::InfoObject &aObj) {
       aObj.DefineProperty("AzureCanvasBackend", GetBackendName(mPreferredCanvasBackend));
       aObj.DefineProperty("AzureSkiaAccelerated", UseAcceleratedSkiaCanvas());
       aObj.DefineProperty("AzureFallbackCanvasBackend", GetBackendName(mFallbackCanvasBackend));
       aObj.DefineProperty("AzureContentBackend", GetBackendName(mContentBackend));

--- a/gfx/thebes/gfxPlatformMac.cpp
+++ b/gfx/thebes/gfxPlatformMac.cpp
@@ -429,21 +429,20 @@ gfxPlatformMac::ReadAntiAliasingThreshol
 bool
 gfxPlatformMac::UseAcceleratedCanvas()
 {
   // Lion or later is required
   return nsCocoaFeatures::OnLionOrLater() && Preferences::GetBool("gfx.canvas.azure.accelerated", false);
 }
 
 bool
-gfxPlatformMac::UseProgressivePaint()
+gfxPlatformMac::SupportsCrossProcessMutex()
 {
-  // Progressive painting requires cross-process mutexes, which don't work so
-  // well on OS X 10.6 so we disable there.
-  return nsCocoaFeatures::OnLionOrLater() && gfxPlatform::UseProgressivePaint();
+  // Cross-process mutexes don't work so well on OS X 10.6.
+  return nsCocoaFeatures::OnLionOrLater();
 }
 
 bool
 gfxPlatformMac::AccelerateLayersByDefault()
 {
   // 10.6.2 and lower have a bug involving textures and pixel buffer objects
   // that caused bug 629016, so we don't allow OpenGL-accelerated layers on
   // those versions of the OS.

--- a/gfx/thebes/gfxPlatformMac.h
+++ b/gfx/thebes/gfxPlatformMac.h
@@ -87,17 +87,18 @@ public:
       // On OS X in a VM, unaccelerated CompositorOGL shows black flashes, so we
       // require accelerated GL for CompositorOGL but allow unaccelerated GL for
       // BasicCompositor.
       return true;
     }
 
     bool UseAcceleratedCanvas();
 
-    virtual bool UseProgressivePaint() override;
+    bool SupportsCrossProcessMutex() override;
+
     virtual already_AddRefed<mozilla::gfx::VsyncSource> CreateHardwareVsyncSource() override;
 
     // lower threshold on font anti-aliasing
     uint32_t GetAntiAliasingThreshold() { return mFontAntiAliasingThreshold; }
 
 protected:
     bool AccelerateLayersByDefault() override;