Why aren't you using Qutebrowser, Zig Forums?
I started using it a couple of weeks ago and honestly I can't imagine going back to Firefox+vimperator/tridactyl.
It's much faster and more responsive than Firefox, it respects the user and the UI is nice, simple and functional.
It uses QtWebEngine in the backend, which is basically ungoogled chromium code wrapped in Qt (wiki.qt.io
It supports greasemonkey scripts (which can be used for user CSS as well), it's got a basic ad blocker and even the web inspector thing.
It's got pretty much everything you'd need and it also has some neat features you never knew you needed like external editor support and whatnot.
There's also an umatrix implementation in development: gitlab.com
Honestly, Qutebrowser is top comfy.
You should try it, especially if you're partial to keyboard driven browsing and are sick of Mozilla and their shit.
Even if you aren't a Vim user and have never used addons like vimperator and whatnot, you should still give it a chance.
You have no idea of the comfyness and efficiency you're missing out on.
The modern web is shit all in all, but Qutebrowser at least makes it bearable, if not somewhat enjoyable to browse.