I'm still sticking with Safari. Firefox's faster, but there's nothing that beats the speed of Safari on Mac, and in addition it is Cocoa (while Firefox is Carbon.) For some reason, this makes Safari feel like a more solid browser, and Firefox feeling like a typical Carbon app (whatever that is - just a weird user experience using it.) If the dealbreaker is extensions, then I have to say that the only extensions I use…
It even has tab-completion, which makes it feel even more solid than what I've experienced with FF and various extensions.
I only open FF for FF-specific testing.