I'm still waiting for one of the main browsers for the Mac to stabilize. Safari is mostly ok, but periodically gets into a confused state - this morning, my wife's Mac stopped being able to deal with Javascript. It was enabled, but wouldn't work until we killed the application and restarted. Very odd.
I had switched to Firefox, but I switched back - it seems very unstable on the Mac, locking up for no good reason more than once per day. On Windows, Firefox is a pig (the developers really, really need to use a decent GC), but it seems mostly stable. On the Mac - not so much.
So I switch back and forth, waiting for stability...