There are many articles about Safari's font rendering, here is one: http://www.joelonsoftware.com/items/2007/06/12.html I think it's more accurate to say that it's different, whether or not it is better seems to be a matter of preference and priorities.
Yes, that was strictly on OS X. I would think that Firefox and Safari would be rendering fonts in the same way, but Safari somehow looks better.
I last compared only a few days ago. When I get back home, I can try again and see if I can get more analytic about what the difference is, but, as I said, part of the problem with this kind of aesthetic/design judgement is that I don't have the vocabulary to analyze it.
I said (or tried to say) above that I was strictly talking about Firefox and Safari on OS X, not on Windows. Upon re-reading, it came out a little funny.