Firefox actually has most privacy stuff you need built-in nowadays. There are surprisingly few steps you need to harden it after install (on both desktop and mobile):
Install the uBlock Origin extension.
Switch Enhanced Tracking Protection to "strict".
Turn on HTTPS-only mode in all tabs.
Optionally:
Switch your search engine away from Google. I've been using DuckDuckGo with zero problems for years, but there are others.
Install the multi-containers extension, it can be used to load websites in isolated color-coded tabs so no data "leakage" can occur.
You do not need any other extension. There is some advanced stuff for fingerprinting protection but they can do more harm than good if you don't know what you're doing. Stick to the above, update Firefox when prompted and that's all.
I love the possibility to have uBlock Origin on mobile. I have Privacy Badger and Decentraleyes installed as well. Toolbar on bottom is another thing I can't live without anymore. That's configurable through settings.
I would add disabling recommendations for Add-Ons and Themes and clearing the initial default bookmarks.
Of course you can pimp it out like setting config properties to enable experimental stuff like Wayland, WebRender, hardware decoding, etc. pp. before they get enabled by default in later releases.
Same, I tried it for a while a few months ago but it never gave me as good results as Google. I'm very aware of the enshittification and will switch away as soon as I notice it not showing me what I want, though.
Yes, it's true uMatrix isn't in dev anymore and supposedly stuff has been incorporated to uBlock but I still feel more at home with uMatrix and it's much more convenient to use and much stricter.
Firefox, and Vivaldi for the occasional site that doesn't work on Gecko. (They're built on the Chromium engine, but absolutely refusing to implement this crap)