Pentadactyl and related plugins, scriptish and stylish, disconnect, ad block edge, xmarks, and a few others. The only thing I actually use firebug for is for a script that automates clicking to play a video and then copy the direct video link from firebug and play it in mpv (which is what I stream all videos in.
I use a lot less extensions since I've switched from chromium to firefox (i find that pentadactyl takes care of most of my needs). On chromium, I really liked tabs outliner, context (as an extension manager), https everywhere, hoverzoom (now I'm just using a user script), and bookmarx.