Note: This method is not available from Web content. It requires elevated privileges to access.
XMLHttpRequest.mozBackgroundRequest is a Boolean, indicating if the object represents a background service request. If
true, no load group is associated with the request, with security dialogs prevented from being shown to the user.
In cases in where a security dialog (such as authentication or a bad certificate notification) would normally be shown, this request fails instead.
Note: This property must be set before calling