code: function addonsManager_undo(aSpec) {
      var spec = aSpec || { };
      spec.link = "undo";
  
      var link = this.getAddonLink(spec);
      this._controller.click(link);
    }
docs: Undo the last action performed for the given add-on
  
  @param {object} aSpec
  Information on which add-on to operate on
  Elements: addon - Add-on element