On 9 November 2004 launched the open source Mozilla-based browser Firefox 1.0. Since then, the browser has been one of the most widely used computer applications in the world. According to various global surveys, the browser now has a market share of nearly 30 percent.
I am not aware of any other open source-based end-user products with multiple users.

Firefox was with e-mail client Thunderbird designed to replace the former Mozilla Suite, SeaMonkey now. Originally, in September 2002, was the browser called Phoenix, but after a name conflict with the BIOS manufacturer Phoenix Technologies, changed the name to Firebird in April 2003. But that name proved to be busy, the open source Firebird database server. The project changed its name after a lot of pressure to Mozilla Firefox in February 2004.
In the U.S., Firefox-name was free, and the Mozilla Foundation registered the trademark in which the software. In the UK the situation was different, but Mozilla was granted a license to use the trademark in Europe by The Charlton Company.
A bit strange is it that the Firefox logo to depict a fox. A "firefox" is actually a red panda. One explanation for this can be found on this page.
Firefox was immediately a success, at least in relation to the objectives Mozilla had set itself. It was partly downloaded almost 10 million times during the first month after laser no.
Later, the browser come in versions 1.5, 2.0, 3.0 and 3.5, all of which introduced new functionality. Now, versions 3.6, 3.7 and 4.0 the next on the road map, as well as a version for mobile phones. In addition, there are a number of smaller patches.
Without in any way to ignore efforts of Norwegian Opera Software has done and still do to promote open Web standards, it is undoubtedly the popularity of Firefox has been great that many Web developers turn their backs to develop websites exclusively for Internet Explorer and instead create sites that works in all major browsers.
It is difficult to find any clear answer to why Firefox has become so popular, for most of the browser originally offered, was already in place in the Opera. Mozilla is no rich organization with large marketing budgets. Most of the revenue is the foundation from Google because the search box in Firefox, where Google is the default search service.
One possible theory is that eventually saw extensive selection of browser add-on that has led to many chose Firefox. The additions give users a great opportunity to customize the browser as desired, and to provide the extended functionality. Firefox was also launched at a time when many experienced Internet Explorer as a big security problem. And Microsoft then showed few signs of making the browser better.
Firefox is based on open source, and has also been important for the popularity, but only in certain environments.
In a recent interview with News.com says Mozilla's technical director, Mike Shaver, that he believes there are about 350 million Firefox users today.
Firefox 'fifth birthday is celebrated in part on this page.