Certainly Firefox is becoming less pleasing and harder to use with each "improvement" (in my opinion); I'm not surprised people are leaving it. I've thought a few times myself of moving on to another. If I could find addons for other browsers like AdblockPlus and Download Helper I probably would.
Firefox appears to be unique in one sense: the addons are often written for the benefit of the user, unlike addons in other browsers which too often are written to benefit big business at the user's expense (again, in my opinion).