Considering the recent FF discussion I figure, why not.
I personally like Chrome and Opera better than FF as far as a vanilla browser goes. But I use FF primarily because it has the richest set of plug-ins, which compensates for me. And I'm guessing I'm not the only one with this thought.
So, what extensions do you often use / have installed? I'm curios to know what other good, useful plug-ins, people use (specifically, I imagine as fellow programmers, you want comparatively similar things out of the web).