Only Mull is good on the FF side. On the Chrome side, use Thorium or Cromite, a fork of the for now dead Bromite.
Avoid Brave, Fennec and IceRaven are not hardened enough. Do not use FF, it dials home. Unless you do the user.js bit with ArkenFox.
As far as usability, but not the best privacy-wise, SmartCookieWeb Preview. Allow to use extensions like unlock just like you do on PC, with the popups at the ready. But it allows for the addons on the address bar.
The term you missed to use was, "echo chambers." Both both and all.