Just gonna say if you’re not happy with the level of customization out of the box for Firefox. You should look into CSS tweaks. Lets you change up a lot about the browser without having to completely switch.
Most CSS tweaks also work on forks as well. I’m personally running LibreWolf + Lepton.
Edit: Should also include to this list of them https://github.com/topics/firefox-tweaks
New desktop environment being made by the Pop_OS devs.