Well, since no one else will say it-I will-I think it'll be crowded, maybe even crazy crowded!
Not only will the locals be there to see the Fireworks but Fantasmic! is premiering on Friday (2 shows).
My suggestion, get there before opening. Grab all the FP you can get (in both parks) so you can use them later in the day/evening.
If you are planning on seeing the fireworks or F! be prepared to wait for a long time and be aware that if you are anywhere near MS before, during, or after the FWs getting around will be time consuming. The CMs will only allow you to go one way. You can also expect a lot of crowds around F!.