Bulb mode = varying shutter speed, depending on how long u press the shutter. if u press for 2 seconds, shutter speed will be 2 seconds. if u press 10 sec, it will be 10 sec. so, for fireworks, use a tripod and use a cable remote if possible, else, use the shutter button on the camera. if u wan the trail of the firework, depress the shutter button when u see the thing flying up and hold it till the fireworks gone. all things that happen within the time the shutter is open will be captured in the camera