Yep, it's the classic self-fulfilling prophecy. Even a lot of non-techies are aware that there are multiple browsers, and will just switch to whichever gets the job done. So if you're seeing less % of any specific browser than the overall web your site is probably broken on that browser. If it's not obvious by now, that means you need to do more testing in that browser, not less.
This. There are some websites that I have to login that are completely broken when using Firefox. I login with Brave on those and am on a constant lookout for competitors that work on Firefox. As soon as I find them I jump ship and take my money elsewhere.
I gave up on Firefox and went back to Blink (via Qutebrowser) in part because of Mozilla's countless recent breakages, regressions, and inexplicable decisions, but in other part because of exactly this problem. So many sites just break in mysterious ways on Firefox, and the reason why is inevitably some exception raised 50 frames down the stack in an obfuscated bundle of $FRAMEWORK_DU_JOUR goop I can't even begin to debug.
It's a nice idea because I think the web is much healthier if we don't have a single dominant browser/engine driving it, whether Microsoft's or Google's or anyone else's. Unfortunately no data I've seen in years says it's actually happening. Every web product I've worked on recently is built on standards first so this has nothing to do with deterring Firefox users because things don't work. There just aren't a lot of people using it any more. The only big browser that isn't running the same engine as Chrome is now iOS Safari.
