I'm thinking of it this way:
It's basically "Men in Black: The TV Show". So in other words, a slightly more chopsocky, less hard sci version of the X-Files.
Think about it.
And of course, you're free to love, hate, or be "meh" about the idea as much as you want. But I'd definitely give it a shot. There's always room in my heart for a cast of Badass Normals inamongst all the supers. And Whedon's quite good at that sort of thing; even in Buffy, only a few members of the gang actually had anything supernatural or otherwise "extra" going for them (enhanced strength and agility; not-particularly-impressive witchcraft; lycanthropy or vampirism that was more annoying than beneficial; part robot, but running off floppy discs...), and it was usually fairly limited and still left them vulnerable in all the other areas. It was little more than an excuse to set up the story in the first place, have a bit of action to break up the episode, and occasionally go off on a complete tangent to everyday reality, in between all the more sitcom type banter that is his hallmark. From what I saw of Firefly, it didn't have ever so much in the way of supers other than River's "engineered killing machine" traits and a couple of the bad guys being just so amazingly evil it was hard to even resist them. It's main "thing" was it was in the future, in space. People still loved it.
And who knows, it might be the SCPesque TV show that Warehouse 13 should've been but couldn't quite manage as it tried to be a little too funny and play up the "its like X-Files but not as serious" side of it, right down to the mismatched guy/girl team who start to crush on each other but never quite see it through.