Yes, there is a carbon version of Mozilla for OS X. It includes Navigator (which evidently is now known as "Mozilla"), Messenger, Composer, etc. I believe it's available from
http://www.mozilla.org; I can't remember exactly where I got it from, but I believe I got it from Mozilla's website.
Having said that, and having used the damned thing for a week or so, I can't even begin to describe how ugly it is. It seems reasonably fast, and not too terribly unstable, but it really looks like it was created by junior high school students. It would look ugly running under gnome or kde; running under the Aqua interface it's just embarrassingly bad. It doesn't even have Mac menus! The menus are contained within windows, à la Windows. It takes no advantage of Aqua; even the scroll bars are really ugly. It seems to do okay with most web pages I've fed it, but it's so hideously ugly, so un-mac-like, so amateurish-looking, that I can't bear to use it.