The logic for enabling / disabling themes (to make sure exactly one theme is active at any time) is spread through XPIProvider.jsm, leading to problems like bug 715680. Perhaps we should refactor this into methods on AddonInternal.

Yeah this code is kinda crazy, mainly because of the need to work with background themes. At one point I know Blair was working on making background themes work with any theme, if that happens this all becomes much much simpler. If that is still on the radar it may be worth just waiting till that happens.

Yea, bug 520124 involves a significant refactor of all the theme stuff - UI and API. Hopefully this bug will be a WONTFIX when that other bug is done (will leave it open until we know so).

Per policy at https://wiki.mozilla.org/Bug_Triage/Projects/Bug_Handling/Bug_Husbandry#Inactive_Bugs. If this bug is not an enhancement request or a bug not present in a supported release of Firefox, then it may be reopened.