I use..
Adblock definitely
Image Zoom (zooming in without saving, among other things)
ieview (for the .1% of webpages I can't use firefox to look at, just right click and open in IE)
Mouse Gestures (use the mouse to open new tabs, switch between tabs, etc. great for laziness)
Tabbbrowser Preferences (more options for tabs versus windows, ie opens external links in new tabs instead of windows)
miniT (lets you reorder your tabs. drag and drop)
all from the extensions link mentioned one post above me