Examine source code of The Mahjong

{
  "manifest_version": 3,
  "name": "The Mahjong",
  "version": "1.0",
  "description": "Discover the Authentic Mahjong in Your Browser!",
  "action": {
    "default_popup": "popup.html"
  },
  "icons": {
    "16": "/assets/icons/16.png",
    "48": "/assets/icons/48.png",
    "128": "/assets/icons/128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "55269a9asdaasdsdasew@themahjong.com"
    }
  }
}