Examine source code of countdown

{
  "name": "countdown",
  "version": "1.0.1",
  "manifest_version": 2,
  "chrome_url_overrides": {
    "newtab": "index.html"
  },
  "icons": {
    "128": "icon_128.png"
  },
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{d8d8bbba-f70f-4d93-aaf0-1bee5d5865f3}"
    }
  }
}