Internet surfers have downloaded the open source Firefox browser more than one billion times, the software's distributor, the Mozilla Foundation, said Friday.

The browser is the strongest current rival to Microsoft's Internet Explorer, which once controlled over 90 percent of the browser market but has seen its dominance steadily eroded by Firefox.

Firefox now accounts for some 22.5 percent of all active browsers, compared to Microsoft's 65 per cent share, according to the tracking firm Net Applications.

Firefox, which grew out of the now defunct Netscape browser in 2004, reached the 500 million download mark just 17 months ago. Its rapid adoption since then could be further accelerated by Microsft's decision to offer users a choice of browsers on all PCs sold in the EU to avoid anti-trust problems by regulators there.

Last year, the foundation set a new world record for the most software downloaded in 24 hours when the third version of Firefox was downloaded more than 8 million times.