Its a modification to an official install of firefox. In firefox you can go into about:config and modify each setting individually. All arkenfox does is set everything for you with a script and you can make an overrides file to tweak their config. See here

For people who don’t want to tweak I generally recommend librewolf. Its a forked firefox client that has quality of life features and ability to change certain settings within your browser’s settings tab. The only downside of using librewolf is updates can fall behind, which can be a security issue. Their team has been on top of updating though.