Examine source code of CookieSync

{
  "manifest_version": 3,
  "name": "CookieSync",
  "description": "Use your Gmail account to sync your game progress across devices, and easily open the game using the extension's convenient button on the extension bar",
  "version": "1.0.0",
  "author": "TheOneAndOnlyDanSan",
  "icons": {
    "128": "icon.png"
  },
  "permissions": [
    "storage",
    "tabs"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://orteil.dashnet.org/cookieclicker/*",
        "http://orteil.dashnet.org/cookieclicker/*"
      ],
      "js": [
        "js/content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "web_accessible_resources": [
    {
      "resources": [
        "/js/inject/*"
      ],
      "matches": [
        "https://orteil.dashnet.org/*",
        "http://orteil.dashnet.org/*"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "cookie@sync.945786"
    },
    "gecko_android": {
      "id": "cookie@sync.945786"
    }
  }
}