It's not part of the Guinness Record download event, but Mozilla just upgraded Firefox 3.0 RC1 to RC2.
Users of the RC1 browser can simply tap 'help' and 'check for updates' to upgrade to the latest Release Candidate of Firefox 3.0.
Some of the features of Mozilla's next generation browser can be found here.
The new download page for Firefox 3.0 RC2 can be found here.