The reason why I harden Firefox forks like Matsumoto Castle is because I try to reduce my browser fingerprint (basically, an profile ID that stays with a browser permanently until a new profile is made). There's a site called fingerprint.com, and it houses some nasty code to basically extract the browser fingerprint... and it's very good at deducing anything you do to the browser, and catches you BSing on what you think your browser is doing.

There are good extensions, like uBlock Origin and NoScript, that allow you to minimize it, but you can't get rid of the espionage entirely.

Compartmentalization basically consists of me using multiple browsers for different purposes. For example, I use LibreWolf as my browser for nostr:nprofile1qy2hwumn8ghj7etyv4hzumn0wd68ytnvv9hxgqgdwaehxw309ahx7uewd3hkcqpqyfg0d955c2jrj2080ew7pa4xrtj7x7s7umt28wh0zurwmxgpyj9sldm58v, Mastadon and #nostr whereas I use Waterfox for regular browsing, Zen Browser for Google shenanigans (I run 3 YouTube channels), and Floorp for a different purpose.