code: function mdObserver_observe(aSubject, aTopic, aData) {
      // Once the window has been found and loaded we can execute the callback
      var window = this.findWindow();
      if (window && ("documentLoaded" in window)) {
        try {
          this._callback(new mozmill.controller.MozMillController(window));
        }
        catch (ex) {
          // Store the exception, so it can be forwarded if a modal dialog has
          // been opened by another modal dialog
          this.exception = ex;
        }
  
        if (window) {
          window.close();
        }
  
        this.finished = true;
        this.stop();
      }
      else {
        // otherwise try again in a bit
        this._timer.init(this, DELAY_CHECK, Ci.nsITimer.TYPE_ONE_SHOT);
      }
    }
docs: Called by the timer in the given interval to check if the modal dialog has
  been opened. Once it has been found the callback gets executed
  
  @param {object} aSubject Not used.
  @param {string} aTopic Not used.
  @param {string} aData Not used.