Examine source code of Geobettr

{
  "manifest_version": 2,
  "name": "Geobettr",
  "version": "1.0.1",
  "description": "Enhance Geoguessr UI",
  "icons": {
    "48": "img/icon-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.geoguessr.com/*"
      ],
      "js": [
        "bundle.js"
      ],
      "css": [
        "css/main.css"
      ]
    }
  ],
  "web_accessible_resources": [
    "img/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{4eae3f04-4cdb-47a8-86f3-a90b99f1ff28}"
    }
  }
}