The quote below is from the official Download Day 2008 website. The guys from Mozilla want to set up a new World record for the most downloads in 1 day.
Set a Guinness World Record
Enjoy a Better WebSounds 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.
If you want to help just click the one of the links above. :)
The download date is not yet known but they will announce it soon. That day will be Firefox 3 launch date.

Firefox 4 ever! I hope that it will get that guiness world record place :X:X it would be sweet, not to mention that we will see the new version