I have been working closer and closer to getting the firework results I've seen elsewhere, created by shifting the lens focus during the exposure. This image I particularly like as it clearly shows the MacDonald Bridge, which the fireworks are fired from.
The challenge of the technique is the lack of predicatability of the firework, combined with only an approximate sense of what the image will look like. In the end, out of hundreds of exposures, only a handful were worth keeping.
With only two large firework displays a year, I do eventually expect to get this technique down to an exact science, but I suspect will be at least another year before I get that far.