Ship torbrowser with a tor-specifc firefox background theme ("Persona")
Firefox supports background themes (previously called "personas") that allow the user to personalize the appearance of the browser window (see [https://en.wikipedia.org/wiki/Firefox_Background_Themes]).
It would be nice if TorBrowser shipped with a tor-specific background theme. This would help users who are running TorBrowser side-by-side with regular Firefox to visually distinguish between the two.
As it stands, the visual similarity between Torbrowser and the interface of a regular Firefox installation means that there is a danger that users might compromise their anonymity/privacy by inadvertently using regular Firefox when they mean to use Torbrowser, and vice versa.