--- a/dom/base/DocumentFragment.h
+++ b/dom/base/DocumentFragment.h
@@ -35,16 +35,17 @@ private:
   }
 
 public:
   using FragmentOrElement::GetFirstChild;
   using nsINode::QuerySelector;
   using nsINode::QuerySelectorAll;
   // Make sure bindings can see our superclass' protected GetElementById method.
   using nsINode::GetElementById;
+  using nsINode::AppendChild;
 
   // nsISupports
   NS_DECL_ISUPPORTS_INHERITED
 
   // interface nsIDOMNode
   NS_FORWARD_NSIDOMNODE_TO_NSINODE
 
   // interface nsIDOMDocumentFragment

--- a/dom/media/TextTrackCue.cpp
+++ b/dom/media/TextTrackCue.cpp
@@ -131,22 +131,23 @@ TextTrackCue::GetCueAsHTML()
   nsPIDOMWindowInner* window = mDocument->GetInnerWindow();
   if (!window) {
     return mDocument->CreateDocumentFragment();
   }
 
   nsCOMPtr<nsIDOMHTMLElement> div;
   sParserWrapper->ConvertCueToDOMTree(window, this,
                                       getter_AddRefs(div));
-  if (!div) {
+  nsCOMPtr<nsINode> divNode = do_QueryInterface(div);
+  if (!divNode) {
     return mDocument->CreateDocumentFragment();
   }
   RefPtr<DocumentFragment> docFrag = mDocument->CreateDocumentFragment();
-  nsCOMPtr<nsIDOMNode> throwAway;
-  docFrag->AppendChild(div, getter_AddRefs(throwAway));
+  IgnoredErrorResult rv;
+  docFrag->AppendChild(*divNode, rv);
 
   return docFrag.forget();
 }
 
 void
 TextTrackCue::SetTrackElement(HTMLTrackElement* aTrackElement)
 {
   mTrackElement = aTrackElement;