The ones I've encountered that appear to bypass Firefox's "no you can't ask" setting are just rendering a mockup of Chrome's, well, chrome over top of the page. It's a pitiful attempt because the UI they're faking looks nothing like the browser I'm actually using (beyond rendering Chrome's UI in a page loaded by Firefox, they'll show Windows OS buttons when I'm using a Mac, or comically they'll do the reverse when Windows is still far and away the most common desktop OS).