You cannot use bulb for nice firework shoots, the explosion might scatter, spoiling the formation.

I shoot them as they explode, it took years of exposure knowledge, precision, timing and knowledge of how firework's work. I usually will fill up the entire frame with the formation when they explode, so the exposure can be good enough to hendheld. Firstly you loose couple of shots to get the exposure reading, use the same reading the copy it in Manual Mode. When the firework launches into the sky you should've half-shuttered, when it explodes into a huge formation just full press the shutter, that's the trick! From then on you can shoot one after another without a problem.

Yeah, it's another way of shooting actually, different way of looking at it. Some do require bulb mode, but you must have good timing and expose setting as well.