To commemorate the moment, the foundation said on its Web site that it would create 50 limited-edition coins, to be distributed to people with stories of spreading the browser online. An additional, a still-unnamed prize will be given to the owner of the Web site responsible for the 50 millionth download.
"It's funny how the counter just blows by 50 million without a care in the world, isn't it?" Mozilla developer Blake Ross wrote on the foundation's Web site. "But it's not just a number to us. It's a validation of half a decade of work, and the beginning of half a decade more."
With its first full-fledged release last November, Firefox has shaken up a Web browser market that most analysts had deemed almost wholly mature. For the first time in years, the market share of Microsoft's Internet Explorer has begun inching downwards as Firefox adoption rises.
Much of the interest in Firefox has been driven by repeated security holes found in Internet Explorer. Some prominent security researchers have even recommended against using IE if possible, a criticism that has stung in Microsoft executive suites.
Indeed, after years of saying that Internet Explorer was inextricably tied to new releases of Windows, Microsoft executives said in February that they would release a new version of IE before the due date of Longhorn, the next planned operating system release. That new version would focus on creating a secure browsing environment, the company said.
However, Firefox itself has begun to show the wear of popularity, with the emergence of several critical security flaws over the past few months. Open-source developers have contended that the browser's architecture is still safer than IE, however.
