nsresult rv;
NS_ENSURE_ARG_POINTER(aDomain); NS_ENSURE_ARG_POINTER(aObserver);
NS_IMETHODIMP nsPref::RemoveObserver(const char *aDomain, nsIObserver *aObserver){  nsresult rv;  nsCOMPtr<nsIPrefBranchInternal> prefBranch = do_QueryInterface(mPrefService, &rv);  if (NS_SUCCEEDED(rv))    rv = prefBranch->RemoveObserver(aDomain, aObserver);  return rv;}