I recently turned on Facebook integration through https://www.facebook.com/about/messenger-for-firefox and now there's no way that I can find to turn it off. Going back to that page asks me to turn it on again. I feel like there must be some way to do it, but I can't find it!
Are you using Nightly or Beta? On mac, there should be a menu item under Tools, but it's not appearing consistently.
Nightly on Linux. Maybe a dupe of bug 804242?
Changing the dupe, it's a bug in nightly
(see also bug 803344 about the more general problem)