nightwatch如何启动firefox

Question

nightwatch的配置如下

// nightwatch.conf.js
const geckodriver = require('geckodriver');

module.exports = (function(settings) {
  settings.test_workers = false;
  settings.webdriver.server_path = geckodriver.path;
  return settings;
})(require('./nightwatch.json'));

// nigthwatch.json
{
  "src_folders" : ["examples"],
  "output_folder" : "output",
  "webdriver" : {
    "start_process": true,
    "log_path": "output",
    "port": 4444
  },

  "test_settings" : {
    "default" : {
      "desiredCapabilities": {
        "browserName": "firefox",
        "acceptInsecureCerts": true
      }
    }
  }
}

同样的配置启动chrome很顺利，启动firefox一点反应也没有，报错也没有，我都无奈了。

官网也说了nightwatch 1.0以上不在需要Selenium Server支持，问题出在哪里？