Since it seems to be a little known tidbit, Mozilla actually has been carbonized and ported to OS X - the port is called "Fizzilla" and can be found here: http://www.mozilla.org/ports/fizzilla. So far, it's working pretty nicely - though its rendering is not as good nor as fast as that of Internet Explorer.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20010413001702401