mozilla.cfg

// skip 1st line
try {

  let {
  classes: Cc,
  interfaces: Ci,
  manager: Cm,
  utils: Cu
  } = Components;

  // set new tab page
  // Cu.import("resource:///modules/AboutNewTab.jsm");
  // var newTabURL_ = "file://<Location to your startpage>";
  // AboutNewTab.newTabURL = newTabURL_;

  // set fx-autoconfig
  let cmanifest = Cc['@mozilla.org/file/directory_service;1'].getService(Ci.nsIProperties).get('UChrm', Ci.nsIFile);
  cmanifest.append('utils');
  cmanifest.append('chrome.manifest');

  if(cmanifest.exists()){
    Cm.QueryInterface(Ci.nsIComponentRegistrar).autoRegister(cmanifest);
    Cu.import('chrome://userchromejs/content/boot.jsm');
  }

} catch(ex) {Cu.reportError(ex)}; // report errors in the Browser Console