1) Lower your ISO. You really want to be down in the 100 range if at all possible.
2) Exposure seemed to be best for me between 2.5 - 3.2 seconds. Basically just long enough to see the flare trail as it was being sent up. Press the button and let the exposure capture it. This differed drastically from everything I had previously been told.
3) f-Stop. I started at a f8 and had to keep lowering it until eventually I was at a running at a f5.
4) IS and AF. Turn them both off. While obvious to turn off Auto Focus, it's not so obvious to turn off Image Stabilization.
Anyways, here are the results after a little time in Lightroom 4.
Canon 6D 70-200 f4 IS USM
93mm, f6.3, 8 sec, ISO 100
Canon 6D 70-200 f4 IS USM
127mm, f5.6, 2.5 sec, ISO 100
Canon 6D 70-200 f4 IS USM
111mm, f5, 2 sec, ISO 100
So those were the highlights. Hopefully I'll get more at some point. We're considering some options to allow more chances at fireworks.
We'll see how it goes. (: