from the firefox site :
Set a Guinness World Record
Enjoy a Better Web
Sounds like a good deal, right? All you have to do is get Firefox 3 during Download Day to help set the record for most software downloads in 24 hours – it’s that easy. We’re not asking you to swallow a sword or to balance 30 spoons on your face, although that would be kind of awesome.
By the way, the official date for the launch of Firefox 3 will be posted here soon – so check back! Join our community and this effort by pledging today.