for me,
i shoot in bulb mode.
F8-12 depending on background.
iso 100.
once i see the stuff being launched i press the shutter down till i see it explode then release..
more or less based on what i want to capture then when i will release the shutter
normally if i want to capture more bursts, i use a higher Fstop.
but too much will be messy too and will get smoke trails.
it will also depend on what type of fireworks to choose the Fstop.