One thing I have not liked about firefox is that it doesn't play that nice with AdSubtract, the ad-blocking proxy I've come to rely on. It works OK with 2.x, but not great under win98se, and really lousy under win xp. And Firefox's relationship with Adsubtract 3.0—which doesn't claim to support anything other than IE, a really retrograde move—is even worse.
All of a sudden, I think I've found the solution. Google took me to dennis.ca, where there is not only a pointer to a firefox plugin for ad blocking, but also a list of adblock filters and host files to prime the pump. I just hope it works half as well as advertised.