I've had a bit of a crisis recently. Although I use FireFox almost exclusively on all platforms, I find that I just can't take it on OS X any more. With the release of 1.5, I've found that FireFox is simply too much of a resource hog on my 1.67Ghz PowerBook G4 with 1.5GB RAM to be usable. Although I never reboot the laptop, I have to quit and restart FireFox every day or so. When the CPU is consistently at 80% utilization, the memory footprint is more than 400MB with about a dozen windows open (no video, no flash), and text field input is delayed by several seconds on a consistent basis, I get agita. The Linux builds don't seem to exhibit this behavior, even under far greater stress.
So, au revoir, FireFox. The promises of a truly integrated OS X build in the 2.0 release may bring me back, but for now, it's Camino all the way.