Safari pre-dated Firefox, so something about your recollection is a bit off here. Perhaps you're thinking of SeaMonkey or Phoenix as the point of comparison?
Either way according to Wikipedia, Don had forked KHTML/KJS in 2001 (which pre-dated the first public release of Phoenix by a year or so), so his choices were to hack SeaMonkey into something suitable or to start from somewhere else.
Either way according to Wikipedia, Don had forked KHTML/KJS in 2001 (which pre-dated the first public release of Phoenix by a year or so), so his choices were to hack SeaMonkey into something suitable or to start from somewhere else.