The Mozilla Firefox project was created by Dave Hyatt and Blake Ross as an experimental branch of the Mozilla project. Firefox 1.0 was released on November 9, 2004. Firefox 1.5 was released on November 29, 2005. Version 2.0 was released on October 24, 2006. Firefox 3.0 was released on June 17, 2008, with Version 3.5 and Version 3.6 released on June 30, 2009 and January 21, 2010 respectively. Version 4.0 was released on March 22, 2011. With Version 5.0 onwards the rapid release cycle was realised which envisions a new major version release every six weeks on Tuesday. The latest version, Firefox 12 was released on April 24, 2012.

The project which became Firefox started as an experimental branch of the Mozilla Suite called m/b (or mozilla/browser). After it had been sufficiently developed, binaries for public testing appeared in September 2002 under the name Phoenix.

The Phoenix name was kept until April 14, 2003, when it was changed because of a trademark dispute with the BIOS manufacturer, Phoenix Technologies (which produces a BIOS-based browser called Phoenix FirstWare Connect). The new name, Firebird, met with mixed reactions, particularly as the Firebird database server already carried the name. In response, the Mozilla Foundation stated that the browser should always bear the name Mozilla Firebird to avoid confusion with the database software. Continuing pressure from the Firebird community forced another change, and on February 9, 2004 the project was renamed Mozilla Firefox (or Firefox for short).