It was certainly his already established style to do drama with snarky comedy, but, he didn't invent it. M*A*S*H* was a Snarky sitcom with lots of Drama, and Blake's 7 (British 1970s SciFi show, that could be said to be an inspiration for Farscape or even Andromeda) was doing Whedonesque Snark long before Whedon even thought about, and that's just two examples off the top of my head, I'm sure there are many examples that could be pointed out.
I missed Firefly in it's initial run, I hadn't even heard of it, until it was almost completely aired. I did catch it later, and do own the box set and Serenity. I enjoy it quite a bit, and think it's a shame it was cut short, because it could've been something really special. I don't think there is enough of it to be referred to "The Best Evah" as some believe, but, it's certainly worth seeing and rewatching, especially since Serenity did tie it up nicely