For several years, Firefox has been my default browser. Firefox’s extensions have always been its paramount feature for me, but its performance and developer tools came close. I’m very happy with it, for the most part.
The one thing that makes me unhappy is Firefox 3’s CPU consumption. Time and again, I find it running at close to full utilization of one CPU core on my MacBook Pro. The tipoff is usually the warmth of the metal case. Killing the Gmail tab tends to help, but not enough. In Firefox 2, the worst problem was the memory leaks. Within hours, it would have chewed up several hundred megabytes. Memory usage is better in FF3, but I still have to shut it down too often for my liking, especially after using Firebug for a while.
In the last couple of months, I’ve been trying other browsers on my MacBook at home. Camino and Safari have had their chances, but they run too hot over time. I’ll be sure to give Chrome a shot when it’s released for the Mac—I quite like it on Windows.