I know this is late...
Depending on your location and what you are trying to achieve, Neutral Density. ND helps tame errant lights. If you are shooting into the sky and just capturing the fireworks, it can help tame some starlight.
I normally try putting something in front like a fountain, statue, memorial, building, etc. It is usually something purpose lit at night. ND helps eliminate inevitable stray lights in the frame and tame local light and allow really long exposures. Alternately you can really silhouette something against a large firework display background. This is challenging because you never really know what you are getting until after. Makes it fun though! Sometimes you get the spectacular!
Obviously, a tripod and remote release method are required.
I've used up to ND1000, 10 stops of ND at ISO 100 and f/7.1.