Debian does package some open-source browser extensions (e.g. uBlock Origin https://packages.debian.org/bullseye/webext-ublock-origin-firefox https://packages.d

Debian does package some open-source browser extensions (e.g. uBlock Origin https://packages.debian.org/bullseye/webext-ublock-origin-firefox https://packages.debian.org/bullseye/webext-ublock-origin-fi...), so you could install extensions that way if you're using Debian or a Debian derivative