https://github.com/arkenfox/user.js There are hundreds of settings that can be configured to harden Firefox. A lot were upstreamed from the Tor Browser via the Tor Uplift project. The afforementioned user.js is well documented and the most well maintained that I'm aware of.

This is one of the leading reasons why I think Firefox is a better browser than competitors because they don't allow this level of customization without hacking on the source code, like say Brave does. However not even Brave or Ungoogled Chromium is hardened as much as Firefox is with this user.js.