Bug 971561 - [System2] Instantiable SystemBanner r=alive

https://bugzilla.mozilla.org/show_bug.cgi?id=971561

Screenshot of JSDoc:

![screen shot 2014-02-13 at 5 47 15 pm](https://f.cloud.github.com/assets/122602/2167480/fa46b17e-9519-11e3-8480-d6b7f0f699bc.png)