A user.js is a configuration file that can control Firefox settings - for a more technical breakdown and explanation, you can read more in the wiki

This is my fork of arkenfox user.js which aims to provide as much privacy and enhanced security as possible, and to reduce tracking and fingerprinting as much as possible - while minimizing any loss of functionality and breakage (but it will happen).

Everyone, experts included, should at least read the wiki, as it contains important information regarding a few user.js settings. There is also an interactive current release, thanks to icpantsparti2.

Also be aware that the arkenfox user.js is made specifically for desktop Firefox. Using it as-is in other Gecko-based browsers can be counterproductive, especially in the Tor Browser.

The arkenfox source repository, literally thousands of sources, references and suggestions. Many thanks, and much appreciated.