Mozilla has announced that Firefox has passed the 400 million download milestone just three years after its launch in November 2004.

The company said that Firefox reached 255 million downloads in September 2006, nearly two years after its launch, and has added another 145 million downloads in the past 12 months, an impressive 56 per cent increase.

Firefox is the main rival to Microsoft's Internet Explorer. Now in its second iteration, Firefox boasts a market share of 28 per cent across Europe and 18 per cent in the UK, according to market watcher Xitimonitor.com.

"The visit share of Firefox 2 is in fact superior to that of Internet Explorer 7 in 16 of the 32 European countries studied," said Xitimonitor.com in its latest browser barometer report.

"But in terms of the level of visit share country by country, the advantage belongs to Firefox 2 to become most popular browser in Europe."

The report also stated that Firefox 2 has imposed itself more widely than other versions of Firefox, than IE7 has with earlier versions of Internet Explorer.

"On average for a European country, Firefox 2 generated 83.2 per cent of Firefox visits for the week July 2 to July 8 2007, whereas IE7 only generated 33.9 per cent of Internet Explorer visits during the same week," said Xitimonitor.com.

The news will be a welcome relief to Mozilla, which announced a raft of changes to its marketing strategy early last month to help improve market share.

"Mozilla has done a reasonably good job getting people to download Firefox, but our data shows that a very high percentage of those people do not become long term, active Firefox users," wrote J T Batson, from Mozilla's marketing team, in a blog posting earlier this year.

"We need to figure out how we overcome the default behaviour of 'clicking on the blue e'."

According to company data posted on a Firefox wiki, approximately half of those who download Firefox never actually install the application.