code: function mdObserver(aOpener, aCallback) {
    this._opener = aOpener;
    this._callback = aCallback;
    this._timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
  
    this.exception = null;
    this.finished = false;
  }
docs: Observer object to find the modal dialog spawned by a controller
  
  @constructor
  @class Observer used to find a modal dialog
  
  @param {object} aOpener
  Window which is the opener of the modal dialog
  @param {function} aCallback
  The callback handler to use to interact with the modal dialog