--- a/layout/painting/nsDisplayList.cpp
+++ b/layout/painting/nsDisplayList.cpp
@@ -1664,17 +1664,17 @@ nsDisplayListBuilder::CreateClipChainInt
 const DisplayItemClipChain*
 nsDisplayListBuilder::CopyWholeChain(const DisplayItemClipChain* aClipChain)
 {
   return CreateClipChainIntersection(nullptr, aClipChain, nullptr);
 }
 
 const nsIFrame*
 nsDisplayListBuilder::FindReferenceFrameFor(const nsIFrame *aFrame,
-                                            nsPoint* aOffset)
+                                            nsPoint* aOffset) const
 {
   if (aFrame == mCurrentFrame) {
     if (aOffset) {
       *aOffset = mCurrentOffsetToReferenceFrame;
     }
     return mCurrentReferenceFrame;
   }
   for (const nsIFrame* f = aFrame; f; f = nsLayoutUtils::GetCrossDocParentFrame(f))

--- a/layout/painting/nsDisplayList.h
+++ b/layout/painting/nsDisplayList.h
@@ -554,34 +554,35 @@ public:
    */
   nsISelection* GetBoundingSelection() { return mBoundingSelection; }
 
   /**
    * @return the root of given frame's (sub)tree, whose origin
    * establishes the coordinate system for the child display items.
    */
   const nsIFrame* FindReferenceFrameFor(const nsIFrame *aFrame,
-                                        nsPoint* aOffset = nullptr);
+                                        nsPoint* aOffset = nullptr) const;
 
   /**
    * @return the root of the display list's frame (sub)tree, whose origin
    * establishes the coordinate system for the display list
    */
   nsIFrame* RootReferenceFrame()
   {
     return mReferenceFrame;
   }
 
   /**
    * @return a point pt such that adding pt to a coordinate relative to aFrame
    * makes it relative to ReferenceFrame(), i.e., returns
    * aFrame->GetOffsetToCrossDoc(ReferenceFrame()). The returned point is in
    * the appunits of aFrame.
    */
-  const nsPoint ToReferenceFrame(const nsIFrame* aFrame) {
+  const nsPoint ToReferenceFrame(const nsIFrame* aFrame) const
+  {
     nsPoint result;
     FindReferenceFrameFor(aFrame, &result);
     return result;
   }
   /**
    * When building the display list, the scrollframe aFrame will be "ignored"
    * for the purposes of clipping, and its scrollbars will be hidden. We use
    * this to allow RenderOffscreen to render a whole document without beign