at http://www.mozilla.org/releases/#1.7.12 there's a download link for the gtk2+xft binary for the mozilla binary. Perhaps the mozilla-bin ebuild should start using this?
sounds like a good idea. I got an idea to make it even better. Instead of just replacing the ebuild, or making a second one to use this binary, why not make it work with the gtk2 and xft USE flags. That way if they are present, it'll fetch the one you just mentioned, and if non present, then it'll just get the old tarball.
Mozilla is dead upstream and will be removed from portage.