Mozilla Firebird is a free, cross-platform, graphical web browser developed by the Mozilla Foundation and hundreds of volunteers. Before its 1.0 release on November 9, 2004, Firefox had already gained acclaim from numerous media outlets, including Forbes [2] and the Wall Street Journal. With over 25 million downloads in the 99 days after its release, Firefox became one of the most used free and open source applications, especially among home users. On August 15, 2006, Firefox had its 80 millionth download, about 10 months after the release of version 1.0.

With Firefox, the Mozilla Foundation aims to develop a lightweight, fast, intuitive, and highly extensible standalone browser forked from the Navigator component of the Mozilla Application Suite. Firefox has become the foundation's main development focus (along with its Thunderbird email client), and has replaced the Mozilla Suite as their official main software release.

Firefox includes an integrated pop-up blocker, tabbed browsing, live bookmarks, support for open standards, and an extension mechanism for adding functionality. Although other browsers have introduced these features, Firefox became the first such browser to achieve wide adoption.

Firefox has attracted attention as an alternative to other browsers such as Microsoft Internet Explorer. As of April 2006, estimates of Firefox's usage share range from 8% to 10% of overall browser usage (see market adoption section), and is even higher on tech-oriented sites frequented by early adopters. Firefox has reduced Internet Explorer's dominant usage share, and may even reignite the browser wars.