I'm a little late to the party here, but wanted to throw in my 2 cents....
First off, everyone complaining about this being revealed on UpUpDownDown doesn't understand the reach this channel has. These are WWE superstars promoting the game, namely Xavier Woods who is a huge fan of fighters. This decision to have UUDD reveal Firestorm is to expose casual players to a game they may know little to nothing about. This is not for us fucking nerds who are trying to breakdown the frame data the moment a trailer drops.
Secondly, judging from what little we see of Firestorm here, I'm fairly disappointed. He was one of the main characters I was looking forward to. Hopefully, there's a lot more to him than we see here. I'm not blown away by his design, either. I was hoping they'd go with a more classic look for him.
Oh well, still super excited for this game and playing as Firestorm either way.