The mobile OS space is already crowded with iOS, Android, Windows Phone, and Blackberry but that's not stopping Mozilla from developing its own. Firefox OS Simulator will let you test out Mozilla's offering without the need for fancy hardware.
Firefox OS Simulator is in an early alpha but it proved to be very stable and usable. The emulator worked flawlessly and didn't crash. There are elements in the emulator that don't look quite right, such as text overlaid on top of other text. This may just be an early (and rough) build of the Firefox OS.
You can download apps from Mozilla's marketplace to test within the Firefox OS Simulator. Apps loaded quickly and functioned much as you would expect apps to function. These apps are basically web applications but feel like native apps.
The Firefox OS Simulator provides an early taste into Mozilla's latest mobile operating system but doesn't offer any features beyond a simulator.