nsresult rv;
nsresult rv; nsCOMPtr<nsILocalFile> file = do_CreateInstance(NS_LOCAL_FILE_CONTRACTID, &rv); NS_ENSURE_SUCCESS(rv, rv);
NS_IMETHODIMP nsPref::GetFileXPref(const char *pref, nsILocalFile **_retval){  nsresult rv;  nsCOMPtr<nsIPrefBranch> prefBranch = do_QueryInterface(mPrefService, &rv);  if (NS_SUCCEEDED(rv))    rv = prefBranch->GetComplexValue(pref, NS_GET_IID(nsILocalFile), (void **)_retval);  return rv;}