--- a/dom/base/Selection.cpp
+++ b/dom/base/Selection.cpp
@@ -1986,17 +1986,17 @@ Selection::SetCanCacheFrameOffset(bool a
 
   // clean up cached frame when turn off cache
   // fix bug 207936
   if (!aCanCacheFrameOffset) {
     mCachedOffsetForFrame->mLastCaretFrame = nullptr;
   }
 }
 
-NS_IMETHODIMP
+nsresult
 Selection::GetCachedFrameOffset(nsIFrame* aFrame, int32_t inOffset,
                                 nsPoint& aPoint)
 {
   if (!mCachedOffsetForFrame) {
     mCachedOffsetForFrame = new CachedOffsetForFrame;
   }
 
   nsresult rv = NS_OK;

--- a/dom/base/Selection.h
+++ b/dom/base/Selection.h
@@ -395,16 +395,20 @@ private:
   // If aVisual is true, this returns caret frame.
   // If false, this returns primary frame.
   nsresult GetPrimaryOrCaretFrameForNodeOffset(nsIContent* aContent,
                                                uint32_t aOffset,
                                                nsIFrame** aReturnFrame,
                                                int32_t* aOffsetUsed,
                                                bool aVisual) const;
 
+  // Get the cached value for nsTextFrame::GetPointFromOffset.
+  nsresult GetCachedFrameOffset(nsIFrame* aFrame, int32_t inOffset,
+                                nsPoint& aPoint);
+
 public:
   SelectionType GetType() const { return mSelectionType; }
   void SetType(SelectionType aSelectionType)
   {
     mSelectionType = aSelectionType;
   }
 
   SelectionCustomColors* GetCustomColors() const { return mCustomColors.get(); }

--- a/dom/base/nsISelectionPrivate.idl
+++ b/dom/base/nsISelectionPrivate.idl
@@ -26,21 +26,16 @@ struct ScrollAxis;
 [ptr] native RangeArray(nsTArray<nsRange*>);
 [ref] native nsPointRef(nsPoint);
 native nsDirection(nsDirection);
 native ScrollAxis(nsIPresShell::ScrollAxis);
 
 [uuid(0c9f4f74-ee7e-4fe9-be6b-0ba856368178)]
 interface nsISelectionPrivate : nsISupports
 {
-    /* GetCachedOffsetForFrame
-     * Returns cached value for nsTextFrame::GetPointFromOffset.
-     */
-    [noscript] void getCachedFrameOffset(in nsIFrame aFrame, in int32_t inOffset, in nsPointRef aPoint);
-
     /**
      * Get the direction of the selection.
      */
     [noscript, notxpcom] nsDirection getSelectionDirection();
     [noscript, notxpcom] void setSelectionDirection(in nsDirection aDirection);
 
     /**
      * Returns the type of the selection (see nsISelectionController for