--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -8433,16 +8433,17 @@ nsCSSFrameConstructor::ContentRemoved(ns
     }
   }
 #endif
 
   nsIFrame* childFrame = aChild->GetPrimaryFrame();
   if (!childFrame || childFrame->GetContent() != aChild) {
     // XXXbz the GetContent() != aChild check is needed due to bug 135040.
     // Remove it once that's fixed.
+    childFrame = nullptr;
     UnregisterDisplayNoneStyleFor(aChild, aContainer);
   }
   MOZ_ASSERT(!childFrame || !GetDisplayContentsStyleFor(aChild),
              "display:contents nodes shouldn't have a frame");
   if (!childFrame && GetDisplayContentsStyleFor(aChild)) {
     if (HasGeneratedContent(aChild)) {
       nsIContent* ancestor = aChild->GetFlattenedTreeParent();
       MOZ_ASSERT(ancestor, "display: contents on the root?");