Photographing fireworks is similar to light trails, much like your fair shots. When possible I use the method described by Chris. the other way use is .
Set you camera to manual mode and lens to manual focus, focus the lens to infinity, iso to 100/200 aperture f11 shutter speed to 2 and 6 seconds, depending on the firework block off light going through your view finder, I use a baseball cap, take your shot using cable release/ or wireless remote,if your camera has mirror lock then this is a good time to use it... Graham
There is nothing worse than a sharp image of a fuzzy concept.. Ansel Adams