Happy Fourth!
How Stuff Works! Fireworks - HowStuffWorks.com is a geek-fest to begin with but if you're one of those people who tore their Etch-a-Sketch all to hell to see how it worked, you'll fall in love with this fount of information.
The first fireworks were actually green bamboo that were thrown into fires to scare spirits away in ancient China, called "pas chuk."
Static electricity in synthetic clothing can ignite fireworks. Those who make fireworks wear cotton all the way down to their underwear.