First off, why do you want to skip it? If you are talking about custom firefight, then there is a way to disable the bonus rounds by going to the game mode options. I don't know exactly where it is, but it's there. If you are talking about matchmaking firefight then I have no idea since I never play it.
He doesn't want to skip the bonus round, he wants to skip all rounds EXCEPT the bonus round. As far as I know, there is no way to skip to the bonus round. You just have to play each round.