docs: function privateBrowsing_start(useShortcut) {
      var dialog = null;
  
      if (this.enabled)
        return;
  
      if (this.showPrompt) {
        dialog = new modalDialog.modalDialog(this._controller.window);
        dialog.start(this._handler);
      }
  
      if (useShortcut) {
        var cmdKey = utils.getEntity(this.getDtds(), "privateBrowsingCmd.commandkey");
        this._controller.keypress(null, cmdKey, {accelKey: true, shiftKey: true});
      } else {
        this._controller.click(this._pbMenuItem);
      }
  
      if (dialog) {
        dialog.waitForDialog();
      }
      this.waitForTransistionComplete(true);
    }