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!
Another for Ublock Origin
Youtube Enhancer
Imagus [enlarges images, great for my old tired eyeballs]
Ad Observer (run by Cybersecurity for Democracy project at New York University, it examines any ads you DO get to look for patterns in how advertising is being used to influence people on social media.)
To Google Translate (Highlight something and send it straight to a Translate page)