Flat Medium Grey
The only change this is /supposed/ do effect is the removal of the vertical lines present when no persona is used.
Text should be black with no shadow, but since shadows are forced and light shadows are terribly dissonant, light text is used.
And since transparent images won't upload, the background color is hard-coded to the precise medium grey of my UI...sorry.
It seems Mozilla hates sharp text and excellent usability as much as it hates terrible usability.