Firestar is a Marvel character, and Starfire is a DC character.
However, they were created only a few months apart, during a time when ripping off the other guy was pretty much business as usual (not that it isn't these days, but at least they pretend to hide it now).
I believe the similarity is coincidental. Yes they're women who can fly and shoot energy out of their hands, but beyond that (and the names) they have little in common.
Firestar's function was to be "the girl" on the team, and to contrast against Iceman.
Starfire's function was wank material: an alien princess who looked like a Boris Vallejo poster, who had been sold into sexual slavery and who gained her powers through a bondage experiment gone awry, and who learns language by French kissing.
Proto-nerds...assuming there have been nerds since there have been humans, I wonder what they were into. Some stone-aged equivalent of Star Trek...some medieval equivalent of test cards...little pointy-haired freaks screaming "By Azura!" every time Joe Codpiece came riding into town on a certain kind of horse...
I don't know. I just know that this comment itself has become incredibly nerdy.