Firefox has a lot of issues
I dunno... I mean, what are your expectations?
Ultimately I have actual problems in my life, my browser choice is an absolutely marginal decision I make when the actual goal is to visit a website that in itself is usually just a tiny component of something else - say ordering something, checking on a piece of information, etc etc.
It's kinda weird to even think so much about browsers - excluding when you are actively developing for/with them - that you recognize issues beyond a single big one like "Has no support for an adblocker". I can get behind that being big enough to matter in regards to which browser is usable or not.
But again, if you develop for Firefox or an addon for it, I can see why details matter and you'd probably have a long laundry list of issues, sure.