--- a/gfx/layers/wr/WebRenderLayerManager.cpp
+++ b/gfx/layers/wr/WebRenderLayerManager.cpp
@@ -366,17 +366,23 @@ PaintItemByDrawTarget(nsDisplayItem* aIt
                       DrawTarget* aDT,
                       const LayerRect& aImageRect,
                       const LayerPoint& aOffset,
                       nsDisplayListBuilder* aDisplayListBuilder)
 {
   aDT->ClearRect(aImageRect.ToUnknownRect());
   RefPtr<gfxContext> context = gfxContext::CreateOrNull(aDT, aOffset.ToUnknownPoint());
   MOZ_ASSERT(context);
-  aItem->Paint(aDisplayListBuilder, context);
+
+  if (aItem->GetType() == nsDisplayItem::TYPE_MASK) {
+    context->SetMatrix(gfxMatrix::Translation(-aOffset.x, -aOffset.y));
+    static_cast<nsDisplayMask*>(aItem)->PaintMask(aDisplayListBuilder, context);
+  } else {
+    aItem->Paint(aDisplayListBuilder, context);
+  }
 
   if (gfxPrefs::WebRenderHighlightPaintedLayers()) {
     aDT->SetTransform(Matrix());
     aDT->FillRect(Rect(0, 0, aImageRect.width, aImageRect.height), ColorPattern(Color(1.0, 0.0, 0.0, 0.5)));
   }
   if (aItem->Frame()->PresContext()->GetPaintFlashing()) {
     aDT->SetTransform(Matrix());
     float r = float(rand()) / RAND_MAX;
@@ -487,16 +493,38 @@ WebRenderLayerManager::GenerateFallbackD
   fallbackData->SetGeometry(Move(geometry));
   fallbackData->SetBounds(clippedBounds);
 
   MOZ_ASSERT(fallbackData->GetKey());
 
   return fallbackData.forget();
 }
 
+Maybe<wr::WrImageMask>
+WebRenderLayerManager::BuildWrMaskImage(nsDisplayItem* aItem,
+                                        wr::DisplayListBuilder& aBuilder,
+                                        const StackingContextHelper& aSc,
+                                        nsDisplayListBuilder* aDisplayListBuilder,
+                                        const LayerRect& aBounds)
+{
+  LayerRect imageRect;
+  LayerPoint offset;
+  RefPtr<WebRenderFallbackData> fallbackData = GenerateFallbackData(aItem, aBuilder, aDisplayListBuilder,
+                                                                    imageRect, offset);
+  if (!fallbackData) {
+    return Nothing();
+  }
+
+  wr::WrImageMask imageMask;
+  imageMask.image = fallbackData->GetKey().value();
+  imageMask.rect = aSc.ToRelativeLayoutRect(aBounds);
+  imageMask.repeat = false;
+  return Some(imageMask);
+}
+
 bool
 WebRenderLayerManager::PushItemAsImage(nsDisplayItem* aItem,
                                        wr::DisplayListBuilder& aBuilder,
                                        const StackingContextHelper& aSc,
                                        nsDisplayListBuilder* aDisplayListBuilder)
 {
   LayerRect imageRect;
   LayerPoint offset;

--- a/gfx/layers/wr/WebRenderLayerManager.h
+++ b/gfx/layers/wr/WebRenderLayerManager.h
@@ -70,16 +70,21 @@ public:
                  mozilla::wr::DisplayListBuilder& aBuilder,
                  const StackingContextHelper& aSc,
                  const LayerRect& aRect);
   already_AddRefed<WebRenderFallbackData> GenerateFallbackData(nsDisplayItem* aItem,
                                                                wr::DisplayListBuilder& aBuilder,
                                                                nsDisplayListBuilder* aDisplayListBuilder,
                                                                LayerRect& aImageRect,
                                                                LayerPoint& aOffset);
+  Maybe<wr::WrImageMask> BuildWrMaskImage(nsDisplayItem* aItem,
+                                          wr::DisplayListBuilder& aBuilder,
+                                          const StackingContextHelper& aSc,
+                                          nsDisplayListBuilder* aDisplayListBuilder,
+                                          const LayerRect& aBounds);
   bool PushItemAsImage(nsDisplayItem* aItem,
                        wr::DisplayListBuilder& aBuilder,
                        const StackingContextHelper& aSc,
                        nsDisplayListBuilder* aDisplayListBuilder);
   void CreateWebRenderCommandsFromDisplayList(nsDisplayList* aDisplayList,
                                               nsDisplayListBuilder* aDisplayListBuilder,
                                               const StackingContextHelper& aSc,
                                               wr::DisplayListBuilder& aBuilder);