Adding icon to Firefox addonbar.
[Firefox] Icon is successfully added to toolbar.
[Firefox] Toolbar icon code is now in its own module.
[Firefox] Making toolbar icon code more functional.
[Firefox] Toolbar icon mostly functional, but giving up on removing it
from currentset.
[Firefox] Changing functionality a bit, no longer bothering to remove icon from currentset.
[Firefox] Making comments more useful. Simplifying code.
[Firefox] Making jshint happy.
Merge pull request #179 from deannah/firefoxButton

Add icon to Firefox toolbar