Using the maximum amount of firework stars in a firework crafting recipe, I attempted to fight the Ender Dragon. I was holding the fireworks in my offhand and using a crossbow with Multishot, Quick Charge III, Unbreaking III and Mending on it. While the rockets would explode on contact with the Ender Dragon and the End Crystals, they would not do any damage whatsoever to either. Normal arrows fired from the same crossbow functioned as they should, damaging both the Ender Dragon and the Crystals. Additionally, I'd tested the fireworks I was using on creepers, spiders, and a Wither, and they did as much damage as one would expect from a firework rocket with the maximum amount of firework stars. I also tested fireworks against the Ender Dragon and Crystals from an unenchanted crossbow and I found that they didn't do any damage either, though again, the fireworks themselves did explode.