Over a year ago, Mozilla announced its plans to work on its own mobile operating system, dubbed Firefox OS. The company officially made a prototype simulator available for developers and anyone curious enough to play around with it (though it's still in early alpha). The OS does take some of Android’s core functionality so it works on Android-capable handsets, but Mozilla also built the UI and application stack around Gecko, the Firefox HTML rendering engine.
Though it’s not technically a 1.0 release, the simulator will make it easier for developers to stay current with future updates to Firefox OS. It's easy to install—all you have to do is download the file from Mozilla and then right-click and open it up in the latest version of Firefox. The browser will then install the Simulator as an add-on. Once it's finished, you'll be able to launch the simulator yourself with a one-click button.