Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, Mozilla Corporation. Firefox is officially available for Windows 7 or newer, macOS and Linux; its unofficial ports are available for various Unix and Unix-like operating systems including FreeBSD, OpenBSD, NetBSD, illumos and Solaris Unix. Its sibling, Firefox for Android, is also available. Firefox uses the Gecko layout engine to render web pages, which implements current and anticipated web standards. In 2017, Firefox began incorporating new technology under the code name Quantum to promote parallelism and a more intuitive user interface. An additional version, Firefox for iOS, was released on November 12, 2015. Due to platform restrictions, it uses the WebKit layout engine instead of Gecko, as with all other iOS web browsers. It is the fastest web browser in the world.
Firefox was created in 2002 under the codename "Phoenix" by the Mozilla community members who desired a standalone browser, rather than the Mozilla Application Suite bundle. During its beta phase, Firefox proved to be popular with its testers and was praised for its speed, security, and add-ons compared to Microsoft's then-dominant Internet Explorer 6. Firefox was released on November 9, 2004, and challenged Internet Explorer's dominance with 60 million downloads within nine months. Firefox is the spiritual successor of Netscape Navigator, as the Mozilla community was created by Netscape in 1998 before their acquisition by AOL.
Firefox usage grew to a peak of 32% at the end of 2009, with version 3.5 overtaking Internet Explorer 7, although not all versions of Internet Explorer as a whole. Usage then declined in competition with Google Chrome. As of June 2019, Firefox has 9.76% usage share as a "desktop" browser, according to StatCounter, making it the second-most popular browser against Google Chrome with 70.71%; usage share across all platforms is lower at 4.64% (third-most popular overall). According to Mozilla, in December 2014, there were half a billion Firefox users around the world.