Addon enable/disable functionality is already in master, in the settings app. Go to Settings > Addons and you'll be able to enable or disable any installed addon. In bug 1131773, I've added additional feature to this Settings panel so that addons can also be deleted, and so that the user can read some information about the addon before deciding to enable or disable it. These features are not in master, yet but have landed on the lightsaber gaia branch. This bug has "Customizer" in the title, but Jacqueline asked for the addon-management features as part of the Settings app. So I suspect that this bug is miscategorized. I'm marking this bug as depending on 1131773 because I think that deleting addons is probably required functionality as well. We've got the feature in the lightsaber branch, so maybe we can close this bug.
Sorry for the mis-filing...updated :)
I see now that bug 1133995 is for enable and disable functionality in the addon manager, so I'll just close this one as a dupe of that one.