Расширения:
RuTracker: https://addons.mozilla.org/ru/firefox/addon/rutracker-add-on/
Bypass Paywalls Clean (D): https://addons.mozilla.org/ru/firefox/addon/bypass-paywalls-clean-d/
Censor Tracker: https://addons.mozilla.org/ru/firefox/addon/censor-tracker/
Chameleon: https://addons.mozilla.org/ru/firefox/addon/chameleon-ext/
Download All Images: https://addons.mozilla.org/ru/firefox/addon/save-all-images-webextension/
EPUBReader: https://addons.mozilla.org/ru/firefox/addon/epubreader/
Firefox Relay: https://addons.mozilla.org/ru/firefox/addon/private-relay/
Side View: https://addons.mozilla.org/ru/firefox/addon/side-view/
Firefox Multi-Account Containers: https://addons.mozilla.org/ru/firefox/addon/multi-account-containers/
Get RSS Feed URL: https://addons.mozilla.org/ru/firefox/addon/get-rss-feed-url/
GIPHY for Firefox: https://addons.mozilla.org/ru/firefox/addon/giphy-for-firefox/
Google Search Fixer (Android only): https://addons.mozilla.org/en-US/android/addon/google-search-fixer/
Image Search Options: https://addons.mozilla.org/ru/firefox/addon/image-search-options/
Music.pro: https://addons.mozilla.org/ru/firefox/addon/musicpro/
Offline QR Code Generator: https://addons.mozilla.org/ru/firefox/addon/offline-qr-code-generator/
Return YouTube Dislike: https://addons.mozilla.org/ru/firefox/addon/return-youtube-dislikes/
Search by Image: https://addons.mozilla.org/ru/firefox/addon/search_by_image/
Web Archives: https://addons.mozilla.org/ru/firefox/addon/view-page-archive/
Buster: Captcha Solver for Humans: https://addons.mozilla.org/ru/firefox/addon/buster-captcha-solver/
Tampermonkey: https://addons.mozilla.org/ru/firefox/addon/tampermonkey/
Translate Web Pages: https://addons.mozilla.org/ru/firefox/addon/traduzir-paginas-web/
To Google Translate: https://addons.mozilla.org/ru/firefox/addon/to-google-translate/
uBlock Origin: https://addons.mozilla.org/ru/firefox/addon/ublock-origin/
CCaptioner: https://addons.mozilla.org/ru/firefox/addon/ccaptioner/
uMatrix: https://addons.mozilla.org/ru/firefox/addon/umatrix/
Video Background Play Fix: https://addons.mozilla.org/ru/firefox/addon/video-background-play-fix/
Worldwide Radio: https://addons.mozilla.org/ru/firefox/addon/worldwide-radio/
Forecastfox: https://addons.mozilla.org/ru/firefox/addon/forecastfox-fix-version/
Video DownloadHelper: https://addons.mozilla.org/ru/firefox/addon/video-downloadhelper/
VK Next: https://addons.mozilla.org/ru/firefox/addon/vk-next-lite/
Voila AI: https://addons.mozilla.org/ru/firefox/addon/voilà-ai-powered-assistant/
Tabliss: https://addons.mozilla.org/ru/firefox/addon/tabliss/
ClearURLs: https://addons.mozilla.org/ru/firefox/addon/clearurls/
Flagfox: https://addons.mozilla.org/ru/firefox/addon/flagfox/

Темы:
Dark Space (animated): https://addons.mozilla.org/ru/firefox/addon/nicothin-space/
Mate Black: https://addons.mozilla.org/ru/firefox/addon/matte-black-v1/
Safari Dark: https://addons.mozilla.org/ru/firefox/addon/safaridark/
Opera GX: https://addons.mozilla.org/ru/firefox/addon/beautiful-opera-gx-fucsia/
Tor: https://addons.mozilla.org/ru/firefox/addon/tor-browser21/
Полезные ссылки:
Firefox CSS Store: https://firefoxcss-store.github.io/
Firefox Addons: https://addons.mozilla.org/ru/firefox/

Сайт с кастомными CSS для изменения интерфейса FF: https://firefoxcss-store.github.io/