FPFF在firefox中的不同名称然后是chrome

I'm using FPDF to create a PDF in PHP. This works fine in Chrome, but doesn't work properly in Firefox.

I'm guessing Firefox is getting this extra number from the URL? This is NOT a big problem, but I would like it to be consistent across browsers. Here is my code:

$pdf = new Fpdf();
$pdf->setTitle("Order-$id");
$pdf->SetAutoPageBreak(FALSE);

Chrome

Firefox