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!
Yeah, when Mozilla killed XUL extensions, he didn’t think there was any way to make it work in WebExtensions. I thought he had quit! I remember having to spend a couple days figuring out how to use Jdownloader for the same tasks. I’m glad he got back on the horse