Firefox OS is an open source mobile operating system developed by Mozilla. It uses open web technologies like HTML5, CSS and JavaScript as its platform instead of relying on native applications. Key components include the Gecko rendering engine, Gaia user interface built with open web technologies, and APIs for common mobile features like telephony, SMS, location and more. Developers can try out Firefox OS using nightly builds or by installing it on supported devices. The open source nature of Firefox OS promotes collaboration through channels like GitHub, IRC and mailing lists.