If you think Firefox is the right choice, and it works 99% of the time, and you're worried about lack of competition... you should probably be using Firefox. That will support its marketshare (by definition).
If you see bugs, you can probably assume they're just regular ol' bugs most of the time. A lot of the web is just plain broken or badly designed.
I'm giving it a shot on my work machine. Device management doesn't give me any options other than Chrome, Edge, Firefox, and Safari anyway. I do like and use Safari for non-work tasks (mainly HN scrolling) but it has some issues that prevent it from being a main browser for me.
So I'll see if I can make FF work but it's mostly cause it's the best option at this point.