Depending on where you are viewing from, you can manage fireworks quite easily with a wide lens, and you do not need anything fast. F8 at 1/2 second ISO 100 will give you nice fireworks motion.
It all depends on weather you are trying to FREEZE action, or show some of the motion. Freezing motion would obviously need faster shutter speed so higher sensitivity and maybe faster apertures..
I wished I was shooting with the Kit lens when I took this as the Fast Fifty was wasted - narrow FoV and no need for fast apertures.