Netscape is just Mozilla repackaged with more bloat. Sea Monkey is almost exactly like Netscape. Firefox is the trimmed down version with a browser only. And Firefox has way less fine tunning options. Yet it is more developed in terms of keeping up with things. One of the most annoying things about firefox is that its cookie control is far inferior, if not just about impossible to control in an easy way. Once you block a site then it is a real hassle to unblock it. SeaMonkey makes that easy.
I have SeaMonkey and use it for particular sites where it is just easier and faster. Other sites work better with FF. Sites that work only with IE I ignored until I got the FF extension for that.