It's a tough spot to be in, for sure.
Firefox used to have two major advantages, at least for me as a user rather than a developer: customisability and the respect for privacy. The former went under a bus with Quantum and has never recovered. The latter is still there, but the single biggest hole in it is the use of Google for search, so that's probably the first thing that many privacy-sensitive users are going to change.
I do still use Firefox as my primary browser, despite having reconsidered several times in recent years. However, as a dev I have all the others readily to hand, and I do find myself forced to use others because pages simply don't work in Firefox with noticeable frequency now. From the opposite angle, I also can't remember the last time a client specified Firefox compatibility for a new project. It's usually Chrome, iOS Safari if mobile is relevant, and maybe Edge in corporate settings now.
Unfortunately the vicious cycle of market share and compatibility has been established, and while I think we'll all end up worse off for it, I'm not sure there's much anyone can do about it at this point, at least not as long as most of the actual functionality in Firefox is (unsurprisingly) so similar to other browsers.
