nsIFrame* thumbFrame = mOuter->GetFirstChild(nsnull);
nsSplitterFrameInner::AddListener(nsPresContext* aPresContext){  nsIFrame* thumbFrame = mOuter->GetFirstChild(nsnull);  nsCOMPtr<nsIDOMEventReceiver>    receiver(do_QueryInterface(mOuter->GetContent()));  receiver->AddEventListenerByIID(NS_STATIC_CAST(nsIDOMMouseListener*,this), NS_GET_IID(nsIDOMMouseListener));  receiver->AddEventListenerByIID(NS_STATIC_CAST(nsIDOMMouseMotionListener*,this), NS_GET_IID(nsIDOMMouseMotionListener));}