Cu.importGlobalProperties(["File"]);

addMessageListener("file.open", function (e) {
  var tmpFile = Cc["@mozilla.org/file/directory_service;1"]
                  .getService(Ci.nsIDirectoryService)
                  .QueryInterface(Ci.nsIProperties)
                  .get('ProfD', Ci.nsIFile);
  tmpFile.append('prefs.js');

  File.createFromNsIFile(tmpFile).then(file => {
    sendAsyncMessage("file.opened", { data: [ file ] });
  });
});
