--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -3902,16 +3902,35 @@ nsLayoutUtils::FirstContinuationOrIBSpli
         break;
       result = f;
     }
   }
 
   return result;
 }
 
+nsIFrame*
+nsLayoutUtils::LastContinuationOrIBSplitSibling(nsIFrame *aFrame)
+{
+  nsIFrame *result = aFrame->FirstContinuation();
+  if (result->GetStateBits() & NS_FRAME_PART_OF_IBSPLIT) {
+    while (true) {
+      nsIFrame *f = static_cast<nsIFrame*>
+        (result->Properties().Get(nsIFrame::IBSplitSibling()));
+      if (!f)
+        break;
+      result = f;
+    }
+  }
+
+  result = result->LastContinuation();
+
+  return result;
+}
+
 bool
 nsLayoutUtils::IsFirstContinuationOrIBSplitSibling(nsIFrame *aFrame)
 {
   if (aFrame->GetPrevContinuation()) {
     return false;
   }
   if ((aFrame->GetStateBits() & NS_FRAME_PART_OF_IBSPLIT) &&
       aFrame->Properties().Get(nsIFrame::IBSplitPrevSibling())) {

--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -1249,16 +1249,23 @@ public:
   /**
    * Get the first frame in the continuation-plus-ib-split-sibling chain
    * containing aFrame.
    */
   static nsIFrame*
   FirstContinuationOrIBSplitSibling(nsIFrame *aFrame);
 
   /**
+   * Get the last frame in the continuation-plus-ib-split-sibling chain
+   * containing aFrame.
+   */
+  static nsIFrame*
+  LastContinuationOrIBSplitSibling(nsIFrame *aFrame);
+
+  /**
    * Is FirstContinuationOrIBSplitSibling(aFrame) going to return
    * aFrame?
    */
   static bool
   IsFirstContinuationOrIBSplitSibling(nsIFrame *aFrame);
 
   /**
    * Check whether aFrame is a part of the scrollbar or scrollcorner of