librewolf for the win, alongside ungoogle chromium
Can't fix the root problem, but it does make it suck less.
Discussion
I'm actually going to test out just switching out my firefox package for librewolf on my laptop tonight. I should be able to copy all the customizations over to it easy too thanks to home manager. That's one of the 3 thing keeping me on firefox. Userchrome, about:config, and container tabs.
My baby. Gruvbox and vertical tabs ftw. Also no titlebar cause that's bloat.
Considering LibreWolf is just a hardened Firefox config preconfigured (for the most part) all three things you've mentioned are present.
And compared to UGC, you don't have to sideload an extension to get the Firefox add-on store working nor deal with Google's malicious fucking up of their browser to advance their business interests. Instead, you deal with the LibreWolf team compensating for Mozilla's ineptitude and smug retardation.