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!
ScrollAnywhere is amazing. I’ve used BetterMouse on Mac for several months now and have grown accustomed to scrolling by click-dragging. Really wish there was some sort of similar app for Windows and Linux, but unfortunately I’ve spent hours searching and haven’t found anything.