parent->FirstChild(aPresContext, nsnull, &nextSibling);
nextSibling = parent->GetFirstChild(nsnull);
GetNextChildFrame(nsIPresContext* aPresContext, nsIFrame* aFrame){  NS_PRECONDITION(aFrame, "null pointer");  // Get the last-in-flow  aFrame = aFrame->GetLastInFlow();  // Get its next sibling  nsIFrame* nextSibling = aFrame->GetNextSibling();  // If there's no next sibling, then check if the parent frame  // has a next-in-flow and look there  if (!nextSibling) {    nsIFrame* parent;    aFrame->GetParent()->GetNextInFlow(&parent);    if (parent) {      parent->FirstChild(aPresContext, nsnull, &nextSibling);    }  }  return nextSibling;}