free open-source (open source) Web browser created by American software company Mozilla Corporation.

In 1998 American Internet-services company Netscape Communications Corp. decided to designate its Navigator browser as open source for users, who began the development of Mozilla Firefox. The Mozilla team, led by American developers Dave Hyatt and Blake Ross, sought to create a light, fast-loading browser that would appeal to users in its efficiency. In 2002 they released their first browser, Phoenix, which soon included features such as bookmarking (for saving Web site addresses) and the ability to add extensions to modify or customize the browser.

Because of trademark disputes with American software company Phoenix Technologies, Phoenix became Firebird. Then in 2004, Firebird was renamed Firefox to avoid confusion with an open-source development project of the same name. The first Firefox (version 0.8) included an installer for Microsoft Corporation's Windows OS ( operating system) and had Google (Google Inc.) as its sole default search engine (users had to add others manually). Soon after the release of Firefox 1.0 in November 2004, the browser began to take a significant portion of the market share from Microsoft's Internet Explorer. Mozilla later expanded Firefox's market worldwide by adding support for 31 languages. (Within weeks of the release of Firefox 1.0, Mozilla also introduced Thunderbird, an open-source e-mail client that was developed to work in tandem with Firefox.) Frequent upgrades to Firefox's security features provide protection against viruses and other malicious software.