I've found that Firefox 2.0 is simply not stable on Mac OS X (10.4.8 Intel). It was locking up on my multiple times a day. I downgraded to 1.5 and have had virtually no problems since (in the last couple of weeks).
Nope, probably stay with Firefox (1.5, until they admit there are Mac OS X problems and fix them). It's much more likely that my clients will be running FireFox than Safari or Opera (my clients, and my client's client's are almost universally running Windows). I think a shift has occured, where people understand that Firefox is the standard, and that IE may take some extra effort "to get working correctly". I'm not saying people don't expect things to run flawlessly in IE ... just that they understand that it's not automatic, that IE makes things harder.