Mozilla is hoping to set a new record for the most downloads over 24 hours ever, and Paul Kim, head of marketing at Mozilla, said: "It's a global effort to make history."
He added that whilst his company had no specific target for the number of downloads it was aiming to get in one day but said that of they get five million it would be "awesome" and already 1.3 million people have promised to download it.
The older Firefox 2.0 registered 1.6 million downloads when it was released on 24 October 2006.
Mozilla Firefox 3 is compatible with Windows 2000, XP and Vista as well as with some non-Windows systems such as Linux.
Version 3 has new features including automatic warnings when users go onto sites booby-trapped with malicious code, and a"Smart Location Bar" that lets people go back to sites they have visited but cannot remember.
