--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -7105,33 +7105,16 @@ nsCSSFrameConstructor::ContentAppended(n
     // XXX the GetContent() != child check is needed due to bug 135040.
     // Remove it once that's fixed.
     MOZ_ASSERT(!child->GetPrimaryFrame() ||
                child->GetPrimaryFrame()->GetContent() != child,
                "asked to construct a frame for a node that already has a frame");
   }
 #endif
 
-#ifdef MOZ_XUL
-  if (aFirstNewContent->GetParent()) {
-    int32_t namespaceID;
-    nsAtom* tag =
-      mDocument->BindingManager()->ResolveTag(aFirstNewContent->GetParent(), &namespaceID);
-
-    // Just ignore tree tags, anyway we don't create any frames for them.
-    //
-    // FIXME(emilio): Is this special-case needed? If we don't create a frame
-    // for them we won't find an insertion point anyway.
-    if (tag == nsGkAtoms::treechildren ||
-        tag == nsGkAtoms::treeitem ||
-        tag == nsGkAtoms::treerow)
-      return;
-  }
-#endif // MOZ_XUL
-
   LAYOUT_PHASE_TEMP_EXIT();
   InsertionPoint insertion =
     GetRangeInsertionPoint(aFirstNewContent, nullptr, aInsertionKind);
   nsContainerFrame*& parentFrame = insertion.mParentFrame;
   LAYOUT_PHASE_TEMP_REENTER();
   if (!parentFrame) {
     // We're punting on frame construction because there's no container frame.
     // The Servo-backed style system handles this case like the lazy frame