Firefox OS is a HTML5 based mobile OS that using it own marketplace Firefox Marketplace.
Not very popular at the moment, but this is a very young OS used commercially for first time by Alcatel and ZTE only a year ago. But as HTML5 improve dramatically every year, and also well known manufacturers also got plans to release Firefox OS mobiles such as LG, personally I can see a lot of potential in Firefox mobiles and in HTML5 in general. As GD already got a html5 engine, in my opinion would be great if GD could make packages that ready to upload to Firefox Marketplace and installed and used on Firefox OS devices. Of course we can upload HTML5 games to anywhere and play them on Firefox OS mobiles in browsers, but the best thing about Firefox Marketplace is that, the HTML5 apps can be installed on Firefox OS devices and played offline.