This method returns a
SettingsLock object. This object is used to access and modify all the settings asynchronously and safely.
Each time you use that method, you add the created lock object to an internal list of
SettingsLock objects. As long as the current
SettingsLock object performs actions against any settings, other
SettingsLock objects will not be able to do anything. All their own actions are queued and will be executed at a later time, one object at a time.
var lock = navigator.mozSettings.createLock();
Not part of any specification yet; however, this API will be discussed at W3C as part of the System Applications Working Group.