Put the bird in the quietest, most insulated room you have, such as in a basement or bathroom or closet, and maybe turn on a radio near his cage so he hears that more than the fireworks.

im so happy fireworks are illegal in my city.

put the bird in the room that you will hear it least. turn on a radio not too quietly but not too loud. cover the cage with a blanket. or you can turn on sounds of cockatiels chirping.

Play some music so the sound of the fire work won't be heard by the birds.

I suggest either go somewhere else or move your bird to a basement? but to be honest the bird should be to freaked, I mean its not as if your doing them in the room beside the bird, that might freak him/her a bit :|

Tommorow I am going to blow up some fireworks myself and I was wondering what can I do to protect my cocktiel from getting freaked out by these loud fireworks and not to mention I don't live in the greatest area so some of these people have illegal fireworks that are extremely loud so any advice will help Thanks