I've just uninstalled firefox 3 not due to the browser itself, but I need a stable version of firebug, and the alpha (which is the only version I could get to work with B5) is buggy and causes the browser to crash. Tis a bit of a shame, but I guess I'll have to wait like everyone else. At least I won't be cursing so much this time around.
My suggestion is if your not using firefox/firebug for development reasons then go ahead. Crashing and all it's not too bad.. unless your debugging.