I posted all the information on another site, but seeing as someone as asked for help I'll post it here. BTW, as for handheld, I've never had good results. Maybe trying to zoom into the explosions may give interesting abstracts, but anything slower than about 1/10th secong (if you're very steady) and you're going to get a lot of camera shake.
A lot of people give links to guides saying use the Bulb setting but I think it is an added complication trying to judge when you have 'enough/too many' explosions. The danger is obviously too many, which if they all explode in a similar place may leave you with a white over exposed blob. emoticon - sad
I think using Bulb is an advanced setting that many people hardly ever use and have little or no experience of, so during a busy display is not the time to experiment as there is a lot to try an remember as it is.
I've found that an exposure of 6 seconds gives time for the firework(s) to rise and then explode. If you have a remote control then timing when to use the shutter is improved, only without a remote control I would consider using the Bulb setting, maybe. But at large displays there are usually enough fireworks to use the timer.
So my little guide for fireworks.
Tripod
Remote Control (should you have one)
Torch
Lowest ISO
Manual Mode
5 - 6 second exposure
f11-f16 maybe higher. Including any interesting scenery such as buildings, bridges etc can add interest, and it is a good idea to set your exposure for the object before the start if it is lit.
White Balance - Tungsten/Incandescent or set for any artificial light in your scene
Flash set to off
Generally Portrait orientation unless there is interesting scenery.
Wear warm clothes.
Try to be familiar with how to change your camera settings before the event as trying to change things in the dark can be stressful, which is why the torch can be useful.
I focus on the 1st explosion, or any practise explosions. Some say set the lens to infinity but I've had soft results when the fireworks were quite a distance away. I normally leave a bit of space at the top of the frame for the higher explosions they tend to throw in. If you zoom in of out I'd focus again. Check your exposure after the first few explosions using the aperture to let more or less light in. If it is a timed display and you know it is coming to an end, maybe because it is set to music, then shut the aperture down 2-3 stops as they tend to throw everything up into the air at the end and you may end up with a big white blob as too many explosions over expose.
Get there early to find a location. Be aware that when the crowds arrive you may have trouble with people knocking your tripod, so find somewhere with space if possible. Make note of the wind direction, you don't want the smoke going into your face.
I've had, and continue to have good results from using the above settings. You may have to slightly adapt depending on your situation, but they are a good place to start imho.
Good luck too anyone who has a go.