Any particular bugs in Firefox bothering you?
The memory leaks that never get fixed. They've gotten a *little* better lately, but FF still sucks down memory from time to like like a process gone rogue. The about:processes page generally don't tell you which tab, but only confirm you do have a problem.
FF just stops working on some pages from time to time while the pages work in Chrome.
Lately there have been more *extras* that have been thrown in, stuff that really doesn't belong in a browser and I have to go hunting to turn them off (e.g. I didn't ask for that weather pop-up and I'd swear I turned it off before but maybe that was on the work computer). Most of the time there is a setting but sometimes you have to go into about:config to really stop them. Their "DNS on HTTPS" broke a few sites at work which was mystifying until I found it and turned it off, because it prevented finding local servers. None of these things is large individually (not even Pocket because it was easy enough to ignore), but it's a large number of annoyances ... as in "death by a thousand cuts".
There are a number of defaults that are annoying, made more annoying because there used to be a setting to control them and make them better (like controlling upgrades) ... but those settings were removed. So now if you're lucky you have to do things to a userContent.css file to "fix them"; or if unlucky then there is no fix. And then FF keeps changing the names or something for no obvious reason because those settings break, and... (it never ends).
Found a icon up top the other day, to quickly bring up extensions, as if the option in the Tools menubar pulldown wasn't good enough. Since I almost never bring up extensions after I do the initial customization I tried to remove it and ... you can't. Why not?
The thing about FF is that it's generally better than Chrome in that you generally have at least some choice ... cue the topic of this article which is a big negative and "kills the user" in 1 blow. OTOH, FF likes to "kill the user" with a thousand little cuts. So with FF at least you survive a little longer, disliking it the whole time.