It was certainly his already established style to do drama with snarky comedy, but, he didn't invent it.
Well no, but my point is the kind of joke/drama blend that Whedon used in Firefly marked it as a Joss Whedon Production. So its approach was basically an expectation
people had for the series going in (in the internet bubble where Buffy
was really popular this show believe it or not had a lot of pre-release hype).