> it was just really heavy and cumbersome because it also had the mail client Communicator and the other stuff like the IRC client and it was very new, very raw, rough-edges software built on this new XPCOM stuff

The suite - Seamonkey - was/is heavy if all you used was the browser. If you compare it to running Firefox and Thunderbird together it actually was quite a bit leaner which is why I ran it for several years on lower-spec hardware.