Try Firefox OS on your Android device as an appBy Shawn Knight
Those wanting to give Mozilla's Firefox OS a try now have another option of going about it. With Firefox OS 2.5 Developer Preview, anyone with an Android device can now try the open-source operating system as a non-destructive app.
All you need to do to get started is download and install Mozilla's APK (you'll want to make sure ahead of time that your phone is set to allow app installations from outside of Google Play). Once installed, simply tap the Home button and you'll be presented with the option to use Firefox OS as an app launcher.
Firefox OS 2.5 includes a number of new features including add-ons, private browsing with tracking protection and a feature called pin the web that lets you pin any site or page directly to your home screen.
Do note, however, that you'll likely encounter some bugs or other odd behavior. After all, you'll be running an operating system on top of an operating system. The Back button in Android, for example, is known to be a bit wonky at times.
Once you've had your fill of Firefox OS, you can simply uninstall it as you would any other launcher.
Up to this point, the only way to try out Mozilla's OS was to either get your hands on a low-end device running the operating system, flash your Android device to permanently run Firefox OS or use the Firefox OS simulator for your PC.