But does it run on Nintendo DSi browser?
Not really relevant anymore, almost everything is chromium nowadays and if you do responsive design in the first place the only thing you gotta test against is Firefox and maybe in some rare cases Safari on a 2 generation old iPad. The rest just works ™
What this meme originally alluded to is the time where it was rather common to check useragent on initial request and serve a completely different site, HTML, CSS, and everything, based on which device you visit from. So you’d have like a site for Chrome, and for Opera, for Firefox, for Edge and every IE, a Mac version, one for iPad, and a separate version for each iPhone model following the everchanging style guides, also a WAP site, a site for playstation, xbox and wii, and also a few Android ones. But the only company I know that still does this is Google, who serves a broken version of it’s search to mobile Firefox users, just because they can.
Try copying an image from image search. On Chrome there’s newer UI where you can long-press an image and save it or copy the url. While on Firefox without addons it opens up a legacy UI that blocks long-presses. You either have to visit the site itself and fish out the image there, or press share, open the link yourself, which opens even older image page, where you can copy the url from “Full-size image” link. Google claims that Firefox lacks some abilities necessary to display Chrome’s UI, but there’s a simple addon called “google search fixer” that just mimics chrome’s user-agent and proves that this is not at all the case.
Or just a service like browserstack, much cheaper and easier than needing 100 devices. Obviously a bit of non-automated real device testing is a good idea too, but most of it should be automated.