I used to have a guitar with Seymour minibuckers, but from what I've read, those are constructed differently than traditional Firebird pickups (IIRC, something about one magnet per pole piece in the Firebird versus just a miniaturized version of the PAF)
I was looking at Lollar Firebird pickups, and he says they sound different than his mini humbuckers.
http://www.lollarguitars.com/mm5/merchant.mvc?Screen=PROD&Store_Code=LGP&Product_Code=242&Category_Code=humbucker-pickups
But if, in general, Firebird pups sound just like any other mini HB, hey, that's good info, too!