Firefox OS is slowly becoming a reality. Within a few days, early next month, anyone will be able to buy a Firefox OS phone, granted the device is aimed at developers mostly. Mozilla is also ramping up efforts to get developers involved, which is crucial.
Mozilla held several hack days this weekend, 20 of them in different countries. If you weren't able to attend, but still want to get started with Firefox OS, there's now a great way to do that with the Firefox OS Boilerplate App, which is exactly what you think it is.
The app is online, so you can check it out in any browser on any device. Of course, it's designed for Firefox OS, so it won't do much anywhere else.
Still, if you're running Firefox OS, on a test phone or in the Firefox OS Simulator, you can install it straight from the web page.
With the app, you can access pretty much all of the phone capabilities made available by the Web API, things like sending an SMS or using the camera.