- Adblock Plus — for blocking ads
- HTTPS-Everywhere — because I like to encourage web site operators to use HTTPS to secure everything, whether it's really necessary or not
- BetterPrivacy — controls cookies
- CookieMonster — more cookie management
- RefControl — controlling the HTTP referer sent
- SkipScreen — skips gateway pages from various file storage/download sites
- Stop Autoplay — stop autoplay of embedded music and movies
- Master Password Timeout — locks the FireFox password archive automatically
- BlockSite — for blocking the sites I like to go to for procrastination purposes. It's amazing how just that little extra effort required to go to those sites can stop me from wasting time. It's almost like typing in "news.ycombinator.com" is just a reflex, and if something is there to block that reflex the amount of procrastination drops significantly!
- Download Statusbar — is a way better way to display current downloads
- FireGestures —mouse gestures control of FireFox
- FEBE — for backing up FireFox settings and plug-ins
- Html Validator — validates HTML web pages. Great for use when marking students web pages!
- TinEye Reverse Image Search — convenient access to TinEye for finding where images came from. Great for checking to see if students submitted web pages with images they copied without permission from elsewhere
(edit: added more ...)