Examine source code of En Garde

{
  "manifest_version": 2,
  "name": "En Garde",
  "version": "1.0",
  "description": "Adds a way to challenge friends quick on Lichess",
  "options_ui": {
    "page": "options.html",
    "browser_style": true
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.lichess.org/*"
      ],
      "js": [
        "index.js"
      ]
    }
  ],
  "permissions": [
    "*://*.lichess.org/*",
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "engarde@squi.cc"
    }
  }
}