docs: function getProperty(url, prefName) {
    var sbs = Cc["@mozilla.org/intl/stringbundle;1"]
              .getService(Ci.nsIStringBundleService);
    var bundle = sbs.createBundle(url);
  
    try {
      return bundle.GetStringFromName(prefName);
    } catch (ex) {
      throw new Error(arguments.callee.name + ": Unknown property - " + prefName);
    }
  }