Adblock Plus + Filterset Updater - Self-updating ad-blocking
DownloadHelper - Youtube vid downloader
Extended Statusbar - Displays amount of data loaded and at what speed in the statusbar
ForecastFox - Tiny and unobtrusive current/forecast weather in the statusbar
Image Zoom - Can zoom any displayed image
PrefBar - Drop-down toolbar that controls various settings, can turn on/off Java, Flash, Sound, Colors, Images, etc, can also Restore Tab, bringing back a tab you closed earlier
SmoothWheel - Smooth page scrolling, you can read clearly while scrolling
Statusbar Clock - Displays date, day of the week, time in the statusbar (my Windows taskbar is set to auto-hide)
Stealther - Traceless browsing. Turn Stealther on, go anywhere, then turn it off - no evidence left anywhere of where you've been
Tiny Menu - Puts all the options at the top of the browser into a single bar, greatly expands viewing space
TryAgain - Load hammers, if a page fails to load, TryAgain will continue trying to load it over and over again.