I do give Firefox a chance, but it gets tiring.
Many years ago, I dropped Firefox's ancestor for Opera 6. The UI and the features were miles ahead (e.g. Mozilla had no tabs). Yet I wanted to support free software so, once in a while, I tried to use Mozilla/Firefox again, but so many features where lacking, and the reactivity was really bad. When Opera dropped their engine and UI to become a new Chromium derivative, I switched to Firefox. I tried to get used to it, but for the past year my main desktop browser has been Vivaldi, a Chromium derivative.
I still use Firefox, but I'm getting more and more irritated against it. I had to search the web in order to change the tile of empty tabs (no buttons, no context menu, only drag-n-drop from bookmarks). Who designed such an unguessable interface?
I can't stand horizontal tabs in my brower. The Tree Style Tab extension was a strong point of pre-quantum FF, though its CPU usage was noticeable. Unfortunately, it's been a pain since I upgraded to Quantum, with many bugs and slowness.
Another example: my last FF ESR upgrade introduced a calamitous rewrite of the download interface. It's inconsistent, error-prone and ridden with several bugs. For weeks, I duplicated many downloads because the notification is absurdly small and quick. Now I've learned to click on the FF icon to check if the download started.
A last example: this morning, I selected 5 finished downloads and removed them. No reaction for 2 seconds, so I pressed the key again, just as the suppression begin, in slow motion. It took FF 3 seconds to remove 6 entries from the log.
With uBlock against tracking, DDG+Qwant for search, and a custom cookie handler (no third-party, white-list for those that persist after a tab closes), I don't think FF has anything to offer me on privacy. So the only reasons that keep me interested in Firefox are Free Software and Web diversity. I'm afraid these moral incentives don't weight much against many practical reasons.