These are a bit unique from the lists everyone else has, I think:
Lemmy Keyboard Navigation (like the kbd shortcuts from RES)
Google Popup Blocker (stop the annoying log in with Google popups everywhere on the web)
OneTab (this one lets you collapse a whole window of tabs down into a list in the OneTab tab that you can later reexpand into a window again when you re-attack whatever subject all the tabs were about)
These are the more standard ones that everyone seems to run: