First of all, install Betterfox, it is not an extension per se, but a set of custom settings. Betterfox offers a lot of fixes, including removed Mozilla telemetry, increased speed, smooth scrolling, privacy protections, etc.
I believe, Betterfox can also be used on Floorp (In case their website doesn’t work, here’s a Github link - https://github.com/Floorp-Projects), which is a Firefox-based browser with Vivaldi/Opera-like interface. Sounds neat, but i didn’t really test it yet.
In case you feel too lazy to install Betterfox/Arkenfox/other user.js modifications, you can use Librewolf instead. It is a version of Firefox with bundled Arkenfox and uBlock Origin.
uMatrix, uBlock Origin, and a mixture of add-ons from Dig Deeper’s list are a must for privacy. Also, i recommend reading his other blogposts about software, too. Especially this one
If configuring Redirector is too confusing for you, you can use LibRedirect, it can automatically redirect YouTube to Invidious and Piped, Fandom to Breezewiki, Google to SearX, Twitter to Nitter, and so on, so you won’t have to bother with popups and ads.
For password managers, use Bitwarden, if you want to have your passwords synced in the cloud, or KeepassXC, if you want to store them locally.
Block The Rich is a fun little extension for those who are tired of reading billionaire spam, but i did not test it.
Instance Assistant Is made to improve Lemmy and Kbin experience, but, once again, i did not test it.
Also, do not use Google, Bing, Yandex or Brave as your search engine, instead switch to DuckDuckGo, Mojeek, and 4Get or SearX
Originally, i too, have thought that Mozilla’s telemetry would be limited to only technical aspects, such as crash reports. I mean, they are using privacy as their main selling point. But of course, that was a lie. Read this. You may think that only Spyware Watchdog and Dig Deeper dislike Mozilla, but no. By searching around, it’s possible to find information about this on countless sources. And again, why do projects like LibreWolf and Arkenfox exist, if Firefox’s tracking is not an issue?
Firefox makes unsolicited connections on startup, uses Google Analytics, and connects to their website when opening every single page. They are not leaking all of your data, like Opera and Chrome do, but such behaviour is very concerning. Why do they need to know how many times i have opened my bookmarks, or when i cleaned my browser history? Extremely suspicious, and on top of that it makes the browser a bit slower.
I believe that what happens on your PC, should stay on your PC, the pages you open in your browser, stay in the browser.