diff --git a/mozilla/layout/base/nsCSSFrameConstructor.cpp b/mozilla/layout/base/nsCSSFrameConstructor.cpp
index c4431939166..3c0ce9ab151 100644
--- a/mozilla/layout/base/nsCSSFrameConstructor.cpp
+++ b/mozilla/layout/base/nsCSSFrameConstructor.cpp
@@ -10965,6 +10965,24 @@ nsCSSFrameConstructor::MaybeRecreateContainerForIBSplitterFrame(nsIFrame* aFrame
     return PR_FALSE;
   }
 
+  // If aFrame is an inline, then it cannot possibly have caused the splitting.
+  // If the frame is being reconstructed and being changed to a block, the
+  // ContentInserted call will handle the containing block reframe.  So in this
+  // case, try to be conservative about whether we need to reframe.  The only
+  // case when it's needed is if the inline is the only child of the tail end
+  // of an {ib} split, because the splitting code doesn't produce this tail end
+  // if it would have no kids.  If that ever changes, this code should change.
+  if (IsInlineOutside(aFrame) &&
+      (
+       // Not a kid of the third part of the IB split
+       GetSpecialSibling(parent) || !IsInlineOutside(parent) ||
+       // Or not the only child
+       aFrame->GetLastContinuation()->GetNextSibling() ||
+       aFrame != parent->GetFirstContinuation()->GetFirstChild(nsnull)
+      )) {
+    return PR_FALSE;
+  }
+
 #ifdef DEBUG
   if (gNoisyContentUpdates || 1) {
     printf("nsCSSFrameConstructor::MaybeRecreateContainerForIBSplitterFrame: "