Wide take-up of the new version would further boost the market share of the browser which is currently used by about 15% of net users.
With the release, Firefox developer Mozilla is attempting to set a record for the most downloads over 24 hours.
"It's a global effort to make history," said Paul Kim, head of marketing at Mozilla.
Net gains
The attempt to break the record will begin at 1800 BST.
"There is actually no record for the greatest amount of software downloaded in one day, so for 24 hours from the moment we push the bits live, that's when the countdown starts," he said.
Mr Kim said Mozilla had no specific target for the number of downloads it would like to achieve on the day but racking up five million would be "awesome".
By comparison, Firefox 2.0 registered 1.6 million downloads on the day it was made available on 24 October, 2006. More than 1.3 million people have pledged to download the new version on 17 June.
WEB BROWSER STATS Internet Explorer - 83.27% Firefox - 13.76% Apple Safari - 2.18% Opera - 0.55% Netscape - 0.14% Source: OneStat |
Also in Version 3 will be "Smart Location Bar" that lets people return to places they have visited even if they have not bookmarked them or cannot remember the full web address.
Firefox 3 will work with Windows 2000, XP and Vista and some non-Windows operating systems including Linux.
Mozilla is not alone in marking the release of the new software. According to the Mozillaparty website more than 566 celebrations are planned for when the software becomes available.
Market battle
Firefox first appeared in early 2004 and since then has steadily eroded Microsoft's hold on the web browsing world.
Although firm statistics are hard to gather Firefox is currently thought to be used by about 15-17% of web users.
In some territories the percentage of Firefox users is far higher. For instance, according to market analysis firm OneStat, 27.23% of German web users browsed the web with Firefox in February 2008. Most of the rest (67.63%) used Internet Explorer (IE).
"Firefox is making very steady encroachment in to the market," said Adam Vahed, managing director of OneStat UK partner Apache Solutions. "It's a very serious contender to the world domination of IE."
He expected there to be great interest in Firefox 3.0 because most users of the browser tend to upgrade to the latest version as soon as it comes out.
By contrast, he said, many people were still using very old versions of IE. According to browser stats gathered by Chuck Upsell about 35% of IE users are on version 7 and 35% use version 6.
Mr Vahed said Firefox was generally popular with more "tech-savvy" web users and they turned to it because using it meant more webpages appeared as their designers intended.
"It's still very much the case that Firefox is way ahead of IE when it comes to standard compliance," he said.
IE's lack of compliance with web standards can make some webpages look very odd, he said.
But, he added, IE7 was better at respecting standards and IE8 is expected to go further.
The second test or "beta" version of IE8 is due in August. The improved standards compliance means that anyone using it might find that pages tailored to work with the quirks of IE7 will now seem broken.
