Examine source code of Site View Showcase

{
  "manifest_version": 2,
  "name": "Top Sites",
  "description": "Shows a list of top sites you've visited.",
  "icons": {
    "32": "icons/logo_32.png",
    "64": "icons/logo_64.png",
    "128": "icons/logo_128.png"
  },
  "version": "1.0",
  "chrome_url_overrides": {
    "newtab": "sites.html"
  },
  "permissions": [
    "topSites"
  ],
  "browser_specific_settings": {
    "gecko": {
      "strict_min_version": "54.0a1",
      "id": "{cf78c608-c656-4786-9f13-ebd029bf2775}"
    }
  }
}