Fix button

* Uses ToggleButton (instead of janky toolbarwidget) in FF29, with a hack to attack the panel to the button.
* Reverts to using SDK's widget for <29, as it has more consistent behavior than toolbarwidget.
* Fixes broken tests (from master).

Fixes #71
(should fix, needs confirmation from reporters since I could not reproduce) #70, #61, #59
(might fix, needs confirmation) #62 

This also helps with #52, but we need the PNGs to be fixed to fully close that one.