But also - it's not high up the priority list given Firefox's marketshare. In most cases, you'll get the support by default, but I don't really see many US managers being tasked with allocating resources to support UC browser, or Opera, and those are both in the same space marketshare-wise.
My management is actively discussing EOLing several Firefox products because we have basically no real paying customers on them, and Mozilla is unpleasant to deal with in the extension space (genuinely - https://www.neowin.net/news/ublock-origin-lite-maker-ends-fi...)
I recently finished a 7 year stint at a company where I was CTO. I always made it clear that we needed to be testing functionality in more than just Chrome because, apart from anything else, a good chunk of our users would be on mobile, and many of those on iOS (i.e., using Safari). I used Firefox as my main browser for probably 4 - 5 of those 7 years, and I suggested engineers do the same because it tends to hew closer to web standards than Chrome does (meaning that if it works in Firefox it'll almost certainly work in Chrome, but the reverse doesn't necessarily hold). That gradually bled through the development team, with a number of the engineers using Firefox as their main browser. That's really all it needs is a few people using it for their day to day work.
I made the change on principle because I could see the way the wind was blowing and - even then - Google were doing plenty of things I didn't like. I like to think that influenced the team as well but, reality check, they probably did it to avoid me moaning at them about bugs running in Firefox all the time.
What I have seen is developers do it wrong to start, then tasks to fix it get low priority due to market share based priority.
The basic mechanic is that the off brand browser has to work hard to be compatible whereas the dominant browser works hard to be incompatible. If you develop Firefox first (have some really ideological devs) you'll find Chrome related bugs eat up 1% of your time if that. If you develop Chrome first you'll find supporting other browsers is a bear.
(In the early 2000's when IE was dominant I was afraid it wouldn't be possible to browse the web with Linux. I worked at a library that would have deployed Sun Rays as public computers if we could get Mozilla to compile on Solaris but we couldn't, even with the help of Sun support. I developed Mozilla-first and then Firefox-first and helped keep the flame alive back then.)
The system I work on now works on both because I develop Firefox-first. There's one screen that loads up 40,000 rows (crazy you say?) worth of data that performs fine on Chrome and is laggy on Firefox, but otherwise the site spins like a top on both of those. Once in a while we run into a serious headscratcher on mobile Safari that burns up some dev*weeks.
Firefox's performance engineers are eager for bug reports! You can record a performance profile [1] and file a performance bug report in Bugzilla [2]. It helps if the slow page is accessible to Firefox engineers for testing, but your performance profile is a big head start.
[1] https://profiler.firefox.com/
[2] https://bugzilla.mozilla.org/enter_bug.cgi?product=Core&comp...
At the time I hadn't thought to go back to tech support and ask somebody there to simply try it with Firefox. Then Verizon would have been pointing fingers at themselves.
Any Verizon developers here? I'd love to know the real story.