browser control message, security wrapper denied access to property _gaUsersPrefs support for expsosing... gradually being removed

A message in browser control that I do not understand. security wrapper denied access to property _gaUsersPrefs on privileged objects. Support for exposing privileged objects to untrusted content via _exposedProps_ is being gradually removed - use WebIDL bindings or Components.utils.cloneInto instead.
 I have no idea what this means or how to do what they recommend, or if this is even a serious issue. There is also another message(2) that might be related. NS_ERROR_APC_SECURITY_Manager_VETO.

Whatever help you can give me in understanding this "new to me" system would be appreciated. I just had Ubuntu, Lennix, firefox installed.