Bug 971561 - [System2] Instantiable SystemBanner r=alive

https://bugzilla.mozilla.org/show_bug.cgi?id=971561

Screenshot of JSDoc:

![screen shot 2014-02-14 at 8 10 18 am](https://f.cloud.github.com/assets/122602/2172382/8e18d396-9592-11e3-8a1b-946efc69f204.png)