Examine source code of New Brand Tab

{
  "manifest_version": 2,
  "name": "New Brand Tab",
  "version": "1.2",
  "description": "Firefox Brand styled new tab page with clock and date.",
  "chrome_url_overrides": {
    "newtab": "index.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{f034f303-e4be-4b27-9f8a-5fb389b7496e}"
    }
  }
}