The 17th June 2008 is Firefox 3 download day. The Firefox team are trying to get into the Guinness book of records with the largest number of downloads within a 24 hour period. I've pledged and will be downloading both a Mac OS X and Windows version during that time.
I didn't do anything special for the last major release - Firefox 2; but for Firefox 1 I donated and had my name included in their 2 page advert in the New York Times in December 2004! I even have this as a poster somewhere!!
Have you made the pledge for Firefox 3?