I just wrote another comment here about its performance, about how I want it to succeed, how I donate to Mozilla, and yet still use a Chromium-based browser due to the performance issues.
At this point (I mean, they've literally invented a new programming language to make it faster, and it's still slow) I think the only thing left to do is to learn C++ and Rust and fix it myself...
It's bugzilla is quite unfriendly, and pretty much everything users wish for is already there, in a ticket that is several years old with no action taken.
An then, the next Firefox version comes with some crappy UX decision made, and it is not configurable. /r/Firefox comes up with _yet another_ userChrome.css tweak to revert it.
And the cycle continues as the user base grows thin. I wonder why.