Examine source code of Fullscreen Clock

{
  "manifest_version": 2,
  "name": "Fullscreen Clock",
  "version": "1.0.0",
  "description": "Shows the current time in the top-right corner when a page enters fullscreen.",
  "icons": {
    "48": "icon.svg",
    "96": "icon.svg",
    "128": "icon.svg"
  },
  "permissions": [
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "defaults.js",
        "content.js"
      ],
      "all_frames": true,
      "match_about_blank": false,
      "run_at": "document_idle"
    }
  ],
  "options_ui": {
    "page": "options.html",
    "browser_style": false,
    "open_in_tab": false
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "fullscreen-clock2@upsuper.org",
      "strict_min_version": "125.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}