While searching for bugs on facebook, i came across one link where you can find deactivated facebook accounts.
The following link should work only to find your deactivated friends but it works for any profile on facebook.
Where “id” is the id of the victim(it can be any id of random facebook user)
and “_user” is your own facebook id
If it returns some js response, that means the profile has been deactivated. if you get blank screen , that means profile is active.
Reported this issue to Facebook but as expected, it doesn’t pose significant privacy/security risk