code: function getDefaultPreferences() {
    if (!defaultPreferences) {
      var contents = fs.readFileSync(WEBDRIVER_PREFERENCES_PATH, 'utf8');
      defaultPreferences = JSON.parse(contents);
    }
    return defaultPreferences;
  }
docs: Synchronously loads the default preferences used for the FirefoxDriver.
  @return {!Object} The default preferences JSON object.