A Linux-based open source operating system from the Mozilla project. Firefox OS runs HTML5-based Web applications and comes with a set of default apps that are part of its Gaia user interface. Several smartphones have been released in more than 30 countries since 2013; however, only a few are available in the U.S. as of 2015. Panasonic was the first to announce the use of Firefox OS as a smart TV interface in certain 2015 models. See HTML5 and Firefox.