code: function privateBrowsing_waitForTransitionComplete(state) {
      // We have to wait until the transition has been finished
      this._controller.waitForEval("subject.hasAttribute('disabled') == false", gTimeout, 100,
                                   this._pbTransitionItem.getNode());
      this._controller.waitForEval("subject.privateBrowsing.enabled == subject.state", gTimeout, 100,
                                   {privateBrowsing: this, state: state});
    }
docs: Waits until the transistion into or out of the Private Browsing mode happened
  
  @param {boolean} state
  Expected target state of the Private Browsing mode