Most of them use Webkit i.e. KHTML, the Zillas use Gecko, Opera has its own, and I think Netscape uses something a bit different from gecko as well. But because they use the same engine(s) does not mean that they support/display things the same way. I prefer Firefox to all of them including Safari, others prefer Camino because it is fast and small.. bleh.. Others live & die by Omniweb. Each one does things the others do not.

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I hate IE 6. Just sayin....