--- a/layout/painting/FrameLayerBuilder.cpp
+++ b/layout/painting/FrameLayerBuilder.cpp
@@ -3892,16 +3892,17 @@ ContainerState::SetupMaskLayerForCSSMask
     return;
   }
 
   int32_t maxSize = mManager->GetMaxTextureSize();
   IntSize surfaceSize(std::min(itemRect.width, maxSize),
                       std::min(itemRect.height, maxSize));
 
   if (surfaceSize.IsEmpty()) {
+    // Return early if we know that the size of this mask surface is empty.
     return;
   }
 
   MaskImageData imageData(surfaceSize, mManager);
   RefPtr<DrawTarget> dt = imageData.CreateDrawTarget();
   if (!dt || !dt->IsValid()) {
     NS_WARNING("Could not create DrawTarget for mask layer.");
     return;
@@ -6276,16 +6277,21 @@ ContainerState::CreateMaskLayer(Layer *a
 
   // maskTransform is applied to the clip when it is painted into the mask (as a
   // component of imageTransform), and its inverse used when the mask is used for
   // masking.
   // It is the transform from the masked layer's space to mask space
   gfx::Matrix maskTransform =
     Matrix::Scaling(surfaceSize.width / boundingRect.Width(),
                     surfaceSize.height / boundingRect.Height());
+  if (surfaceSize.IsEmpty()) {
+    // Return early if we know that the size of this mask surface is empty.
+    return nullptr;
+  }
+
   gfx::Point p = boundingRect.TopLeft();
   maskTransform.PreTranslate(-p.x, -p.y);
   // imageTransform is only used when the clip is painted to the mask
   gfx::Matrix imageTransform = maskTransform;
   imageTransform.PreScale(mParameters.mXScale, mParameters.mYScale);
 
   nsAutoPtr<MaskLayerImageCache::MaskLayerImageKey> newKey(
     new MaskLayerImageCache::MaskLayerImageKey());