If your tanks not 10' long... Quickly take your tank apart, take out the tang and return it to the store you got it from. Tell them that they should have never sold it to you, than tell them how to run their business and what you think they should and should not sell. Don't ever go back there again.
The firefish should be fine as soon as they find a spot where they can dart to and hide. With changing your rockwork it should also help with the aggressive behavior your tang is showing. Everything should be fine in a day or two.