For compatibility reasons, mozilla.org mozilla is compiled against the older gtk1, which doesn't do anti-aliasing.
There's a mozilla 1.7.2 in Fedora updates: why not use that one? (I had a feeling that mozilla.org had started to offer gtk2 builds, but I can't find them now. I used to compile my own to get around the lack of GTK2 updates.)
here: ftp://ftp.mozilla.org/pub/mozilla.org/mozilla/yum/SeaMonkey/releases/
