Seamonkey is much older, and not really a fork as it follows current day Firefox development quite closely. Hell, one may well call Firefox a fork of the brows

Seamonkey is much older, and not really a fork as it follows current day Firefox development quite closely. Hell, one may well call Firefox a fork of the browser part of Seamonkey. A more interesting comparison to Waterfox would be Pale Moon. And there is also Basilisk, a more recent project by the Pale Moon people.