Ublock Origin is an obvious one, but I also can’t stand not having Foxy Gestures anymore. It adds customizable mouse gestures, so you can set it up to have easy swipes to go back a page, reload a page, close a tab, etc, and it feels wonderful and smooth to use compared to just using the traditional buttons to do everything. Honestly it’s kinda wild to me that this isn’t more popular now that people are so used to phone gestures. It’s good for the same reasons!
Firefox Multi-Account Containers is one of my favorite extensions. Mixing work accounts and personal accounts in the same browser session but in different tabs has made my workflow much more efficient. You can force bind sites to a container so that you don’t accidentally use your personal account for anything workplace related.
This one. I need to use Farcebook occasionally and this allows me to stay logged in without getting tracked elsewhere. Same for my Google account.
Have you figured out a way to combine it with windows, such that each window has a designated container, and all tabs open in that container?