Examine source code of Customizable Start Page

{
  "manifest_version": 3,
  "name": "Customizable Start Page",
  "version": "1.0",
  "description": "Design a personalized homepage with widgets and shortcuts.",
  "permissions": [
    "storage"
  ],
  "chrome_url_overrides": {
    "newtab": "index.html"
  },
  "action": {
    "default_icon": {
      "128": "icons/icon-128.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{b6e5a9c1-8d6e-4d7e-9f3c-6b8f93dfd9cd}"
    }
  }
}