For fireworks, you would be better off getting a fireworks CD and doing some desensitizing training.
The shirts work, but only when you are around to put one on and they don't deal with the root cause of the problem.
The CD is just lots of noises of fireworks
You start off with it on a very low volume when your dog is eating, or you are doing something fun like playing with a toy.
Then over the course of several weeks, you turn the volume up and up and up.
The dog associates the noise of fireworks with something nice, and it also learns there is nothing to be scared of.
They aren't as effective with thunder storms as fireworks, because storms bring atmospheric changes that dogs can sense, so get more worried than with a noise alone.
But it is definitely definitely worth trying
You can buy the CDs online, and they will come with full instructions on how to use them (and what to do if your dog isn't responding well at first)
I've used them a couple of rescue dogs I've had as well as dogs I've helped train, and I've never met a dog who doesn't improve after it. The worst thing that can happen is that you'll have to take it slowly and it takes months rather than weeks, but the effects are permanent