Mozilla Firefox (or simply Firefox) is a free and open-source web browser developed by Mozilla Foundation and its subsidiary, Mozilla Corporation. Firefox is available for Windows, macOS, Linux, and BSD operating systems. Its sibling, Firefox for Android, is available for Android. Firefox uses the Gecko layout engine to render web pages, which implements current and anticipated web standards. In 2016, 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 in late 2015, due to platform restrictions, it uses the WebKit layout engine instead of Gecko, as with all other iOS web browsers.
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 in November 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, temporarily making version 3.5 the world's most popular browser. Usage then declined in competition with Google Chrome. As of March 2018, Firefox has 11.6% usage share as a "desktop" browser, according to StatCounter, making it the second most popular such web browser; usage across all platforms is lower at 5.44% (and then 4th most popular overall). Firefox is still the most popular desktop browser in Cuba (even most popular overall at 62.77%) and Eritrea with 78.3% and 82.96% of the market share, respectively. According to Mozilla, as of December 2014 there were half a billion Firefox users around the world.