code: function(err) {
            var self = this;
            if (!self.$isDestroyed) {
              self.$isDestroyed = true;
              self.$$conf.sync.destroy(err);
              self.$$conf.binding.destroy();
              $firebaseUtils.each(self, function (v, k) {
                delete self[k];
              });
            }
          }
docs: Informs $firebase to stop sending events and clears memory being used
  by this object (delete's its local content).