code: public static XpiDriverService createDefaultService() {
      try {
        return new Builder().build();
      } catch (WebDriverException e) {
        throw new IllegalStateException(e.getMessage(), e.getCause());
      }
    }
docs: Configures and returns a new {@link XpiDriverService} using the default configuration. In
  this configuration, the service will use the firefox executable identified by the
  {@link FirefoxDriver.SystemProperty#BROWSER_BINARY} system property on a free port.
  
  @return A new XpiDriverService using the default configuration.