Shutter speed controls the speed at which the shutter opens and closes. How slowly or quickly the shutter is released allows more or less light in to expose the image. For night shots, use a long exposure! It allows you to expose in this low light situation and helps to incorporate the movement of fireworks.
What shutter speed should you put your camera on? Try 1″, 2″ or 4″ seconds. Press the shutter just as the firework is about to explode. Experiment! But don’t keep your shutter open too long. It won’t take much to over expose your images.
Will you experiment and try this?