Examine source code of custom start page

{
  "manifest_version": 2,
  "name": "new tab",
  "description": "new tab page",
  "version": "1.3.2",
  "content_security_policy": "script-src 'self' 'sha256-WOdSzz11/3cpqOdrm89LBL2UPwEU9EhbDtMy2OciEhs=' https://ajax.googleapis.com/;  object-src 'self'",
  "chrome_url_overrides": {
    "newtab": "index.html"
  },
  "permissions": [
    "bookmarks"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{b97776df-922a-4ee9-8a85-708f5c6bb83b}"
    }
  }
}