Tbh, I don’t use that many plugins either. Besides U-Block I got:
Plasma Integration so I can search bookmarks via KRunner;
Dark Reader because I don’t like bright colours;
Gesturify because I love mouse gestures;
Some translator (I’ve forgotten their name)
Simple Tab Groups to stay organized;
Progressive Web Apps for Firefox (but I’m currently testing which plugin works best)
Honorable mention: Tab Discard, which I used to have but Firefox kinda has something similar now (or at least Floorp has, they also got their own Workspaces so I also don’t need STG any more)