Want to take Mozilla's upcoming Firefox OS for a spin? You're in luck, because the developers have released a simulator called "r2d2b2g", or b2g for short, that allows you to install an .xpi extension inside of a desktop version of Firefox and see what it is that Mozilla has up its sleeves.
Once the .xpi is installed, you'll be greeted to a dashboard (seen below) where you'll be able to turn the simulator on and get into action. A pop-up window will appear with a recent build of Firefox OS running inside of it. As a simulator, you'll be able to use the OS inside of this pop-up much like you would on a regular phone. This simulator isn't like a virtual machine, where functionality is cut-off. Instead, it's full-featured, and capable of even going online thanks to the base the desktop Firefox provides behind it.
Once into the OS, you can swipe left and right (with your mouse, or by touch) to peruse it like any other. On the first left is an apps list, which appears to be where things can be installed. Nothing I tried to use here would function. The opposite could be said when you move right towards the homescreen, where many expected apps can be found. For developers who are using this for more than just a toy, certain testing-related apps can be found as well.
For the most part, this simulator is pretty stable, although I did have it crash twice within the span of a couple of minutes. It's still worth checking out if you want to see what it is Mozilla's been working on all these months, and I do admit I'm pretty satisfied with what's here. It's not going to take over iOS, Android or the other mobile OSes anytime soon, but that's not really Mozilla's goal. Instead, this OS should power some of the most affordable phones on the planet, getting them into the hands of those who either can't or don't want to splurge on an expensive model. Plus, more than any other, Mozilla has a major emphasis on open-source with Firefox OS, which could be appealing to those who consider even Android to be rather restrictive.