override-echo.js

const stackPattern = /(zip-de-download|hoge)\.js/;

function popupAlert (iconPath, title, text, buttonEnabled, a, b) {
  const ALERT_SVC =
    Components.classes["@mozilla.org/alerts-service;1"].
      getService(Components.interfaces.nsIAlertsService);
  ALERT_SVC.showAlertNotification.apply(ALERT_SVC, arguments);
}

function simplePopupAlert (title, text) {
  return popupAlert("", title, text, false, null, null);
}

let U = plugins.libly.$U;
U.around(
  liberator,
  'echo',
  function (next, args) {
    let [msg] = args;
    try {
      if (new Error('meow').stack.match(stackPattern))
        simplePopupAlert('', msg);
    } catch (e) {
      liberator.log(e);
    }
    return next();
  }
);