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!
Thanks so much for sharing this extension. I was looking for something that worked better than the tab tree extension I was using. I also found a way to custom edit the userChrome.css to hide the top tab bar—which really makes Firefox feel like Opera. Love that.