--- a/layout/generic/ViewportFrame.cpp
+++ b/layout/generic/ViewportFrame.cpp
@@ -177,16 +177,21 @@ ViewportFrame::BuildDisplayListForTopLay
         BuildDisplayListForTopLayerFrame(aBuilder, backdropFrame, aList);
       }
       BuildDisplayListForTopLayerFrame(aBuilder, frame, aList);
     }
   }
 
   nsIPresShell* shell = PresShell();
   if (nsCanvasFrame* canvasFrame = shell->GetCanvasFrame()) {
+    // Build display items for the dropped-down menu
+    if (nsIFrame* dropdownFrame = canvasFrame->GetDropdownFrame()) {
+      BuildDisplayListForTopLayerFrame(aBuilder, dropdownFrame, aList);
+    }
+
     if (Element* container = canvasFrame->GetCustomContentContainer()) {
       if (nsIFrame* frame = container->GetPrimaryFrame()) {
         BuildDisplayListForTopLayerFrame(aBuilder, frame, aList);
       }
     }
   }
 }
 

--- a/layout/generic/nsCanvasFrame.cpp
+++ b/layout/generic/nsCanvasFrame.cpp
@@ -251,16 +251,25 @@ nsRect nsCanvasFrame::CanvasArea() const
   if (scrollableFrame) {
     nsRect portRect = scrollableFrame->GetScrollPortRect();
     result.UnionRect(result, nsRect(nsPoint(0, 0), portRect.Size()));
   }
   return result;
 }
 
 void
+nsCanvasFrame::SetDropdownFrame(nsIFrame* aDropdownFrame) {
+  if (aDropdownFrame) {
+    MOZ_ASSERT(aDropdownFrame->IsListControlFrame(),
+               "Only nsListControlFrame can be dropped down.");
+  }
+  mDropdownFrame = aDropdownFrame;
+}
+
+void
 nsDisplayCanvasBackgroundColor::Paint(nsDisplayListBuilder* aBuilder,
                                       gfxContext* aCtx)
 {
   nsCanvasFrame* frame = static_cast<nsCanvasFrame*>(mFrame);
   nsPoint offset = ToReferenceFrame();
   nsRect bgClipRect = frame->CanvasArea() + offset;
   if (NS_GET_A(mColor) > 0) {
     DrawTarget* drawTarget = aCtx->GetDrawTarget();

--- a/layout/generic/nsCanvasFrame.h
+++ b/layout/generic/nsCanvasFrame.h
@@ -33,16 +33,17 @@ class nsCanvasFrame final : public nsCon
                             public nsIScrollPositionListener,
                             public nsIAnonymousContentCreator
 {
 public:
   explicit nsCanvasFrame(nsStyleContext* aContext)
     : nsContainerFrame(aContext, kClassID)
     , mDoPaintFocus(false)
     , mAddedScrollPositionListener(false)
+    , mDropdownFrame(nullptr)
   {}
 
   NS_DECL_QUERYFRAME
   NS_DECL_FRAMEARENA_HELPERS(nsCanvasFrame)
 
 
   virtual void DestroyFrom(nsIFrame* aDestructRoot, PostDestroyData& aPostDestroyData) override;
 
@@ -108,26 +109,33 @@ public:
 #ifdef DEBUG_FRAME_DUMP
   virtual nsresult GetFrameName(nsAString& aResult) const override;
 #endif
   virtual nsresult GetContentForEvent(mozilla::WidgetEvent* aEvent,
                                       nsIContent** aContent) override;
 
   nsRect CanvasArea() const;
 
+  // The frame should be dropped down
+  nsIFrame* GetDropdownFrame() const { return mDropdownFrame; }
+  void SetDropdownFrame(nsIFrame* aDropDownFrame);
+
 protected:
   // Utility function to propagate the WritingMode from our first child to
   // 'this' and all its ancestors.
   void MaybePropagateRootElementWritingMode();
 
   // Data members
   bool                      mDoPaintFocus;
   bool                      mAddedScrollPositionListener;
 
   nsCOMPtr<mozilla::dom::Element> mCustomContentContainer;
+
+private:
+  nsIFrame* mDropdownFrame;
 };
 
 /**
  * Override nsDisplayBackground methods so that we pass aBGClipRect to
  * PaintBackground, covering the whole overflow area.
  * We can also paint an "extra background color" behind the normal
  * background.
  */