San Francisco, Nov 10 (DPA) The open source internet browser Firefox marked its fifth anniversary Monday, celebrating its rise from an unknown challenger to Microsoft's Internet Explorer to a formidable competitor that has been downloaded over one billion times by 330 million users around the world.

"Over the last five years we've been setting ourselves up for the next five. The web is moving faster, not slower, and modern browsers are set to handle it," said Chris Blizzard of the Mozilla Foundation.

The browser was built up from the Netscape browser that Microsoft put out of business, and has enjoyed a measure of revenge by effectively breaking the monopoly of Internet Explorer which enjoyed over 95 percent market share when Firefox was first released.

Now Firefox has a market share of around 25 percent market, even though it faces increased competition.

"With additional entrants, most notably Google and Apple, joining the fray there's a massive amount of competition in the browser market that is fuelling constant innovation and envelope pushing, from speed and features to the development of the mobile browser," Mozilla said in a statement.

Mozilla said it continued to be guided by its original philosophy - that the internet is a public resource that should be as accessible and open as possible. It plans to release the fourth major upgrade to Firefox next year along with a mobile Firefox version called Fennec.