nsIFrame* firstChild; aFrameItems.containingBlock->FirstChild(aPresContext, aChildListName, &firstChild);
nsIFrame* firstChild = aFrameItems.containingBlock->GetFirstChild(aChildListName);
static nsresult InsertOutOfFlow(nsIPresContext* aPresContext,                                const nsAbsoluteItems& aFrameItems,                                nsIAtom* aChildListName) {  if (!aFrameItems.childList) {    return NS_OK;  }  nsIFrame* firstChild;  aFrameItems.containingBlock->FirstChild(aPresContext, aChildListName, &firstChild);  // Note that whether the frame construction context is doing an append or  // not is not helpful here, since it could be appending to some frame in  // the middle of the document, which means we're not necessarily appending  // to the children of the containing block.  //  // We need to make sure the 'append to the end of document' case is fast.  // So first test the last child of the containing block  nsIFrame* lastChild = nsLayoutUtils::GetLastSibling(firstChild);  if (lastChild) {    if (nsLayoutUtils::CompareTreePosition(lastChild->GetContent(),                                           aFrameItems.childList->GetContent(),                                           aFrameItems.containingBlock->GetContent()) < 0) {      // lastChild comes before the new children, so insert after lastChild      return aFrameItems.containingBlock->        AppendFrames(aPresContext, *(aPresContext->PresShell()),                     aChildListName, aFrameItems.childList);    }  }  nsIFrame* insertionPoint = nsnull;  // try the other children  for (nsIFrame* f = firstChild; f != lastChild; f = f->GetNextSibling()) {    if (nsLayoutUtils::CompareTreePosition(f->GetContent(),                                           aFrameItems.childList->GetContent(),                                           aFrameItems.containingBlock->GetContent()) > 0) {      // f comes after the new children, so stop here and insert after      // the previous frame      break;    }    insertionPoint = f;  }  return aFrameItems.containingBlock->    InsertFrames(aPresContext, *(aPresContext->PresShell()),                 aChildListName, insertionPoint, aFrameItems.childList);}