Even with the latest release of Firefox out for OS X users, Safari and Chrome are still very much something that remains on the radar. And obviously for OS X users, Safari is never far from anyone’s mind when it comes to a strong browser right out of the gate.
As for what is making Firefox 3.5 such a hit, that is difficult to explain. On my Linux box, it’s performance is vastly improved. And on the Mac, I have also noted some improvement there as well. Firefox does seem to run a bit smoother. Enough to where I am not reaching for alternatives as often, anyway.
As to whether the new found competition with Chrome is going to eventually be an issue, I would remind everyone it is too early to know yet. Ask me again in a year or so, then I should have a better idea on this one I suspect. Because thus far, Chrome is not a threat to anyone.