The new version of Firefox may allow tabs to run across the top

The open-source browser Firefox passed its billionth download on Friday, ahead of the release of its fourth iteration.

The milestone includes downloads of all versions of the web software since its first release in 2004.

Figures suggest that Firefox now has nearly one third of the browser market worldwide, at 31%.

Microsoft's Internet Explorer still dominates the field with around 60%, whilst Google's Chrome, Apple's Safari and Opera are all less than 5%.

Microsoft is currently in talks with the European competition regulators, which ruled in January that pre-bundling Internet Explorer with the company's Windows operating system hurt competition.

The firm recently made a proposal that would offer European buyers of its new Windows 7 operating system a list of potential browsers when they first install the software.

Regulators in Brussels said they "welcomed" the proposal but have yet to make a decision.

Firefox would be among the browsers on offer.

Record run

The browser, developed by the Mozilla Foundation, has quickly become a favourite with web surfers since its launch in 2004.

Last year, the foundation set a new Guinness world record for the most software downloaded in 24 hours when the third version of Firefox was downloaded more than eight million times.

The billionth download figure includes all versions of Firefox released since 2004 and includes single users downloading multiple copies for different computers.

In addition, the figure includes anyone manually updating their software to the latest version, rather than waiting for the automatic download.

Automatic updates are not included in the total.

The total number of downloads can be tracked on the Mozilla website. The foundation plans to launch a new website, OneBillionPlusYou.com, to celebrate the milestone.

Mozilla developers are currently working on the fourth iteration of the software.

Earlier this week, it showed off screenshots of the next version of the browser, Firefox 4.0.

The images showed a browser with a similar look to Google's Chrome software.