Why ask people who use Firefox to defend it to you? You already know Firefox, so you know what its redeeming qualities are.
You have two major options:
1) Figure out how to make Firefox livable for you on a Mac... if this is what you want, focus on what you want (speed, anything else?) and let people specifically help you with any tricks to make Firefox faster. Like evaluating whether you want to try a Firefox 3 alpha/beta, some configural or plug-in tricks, etc....
2) If you don't think you can live with FF, then ask about the things you want and how you can get them in another browser, to determine if you should migrate to Safari, Opera, Camino, Shiira, or another browser.
But it seems to me that having people defend Firefox/Mac to you is just silliness.
FWIW, legal disclosure, I rarely use Firefox/Mac (in spite of using it routinely on Windows) because I prefer Safari 3.