I should start by saying that Firefox has all but driven me away. I can no longer ignore the way the performance has continued to deteriorate with successive versions. I'm almost ready to switch to something else until they get their act together. But the fact is that, for me, what Firefox offers is really hard to beat.
So this is my list of must-haves before I'll consider using another browser setup on a regular basis. I'm a professional web developer, and like many people reading this, I'm also an internet junkie. So this isn't going to be the typical feature set.