Examine source code of Custom URL New Tab

{
  "manifest_version": 3,
  "name": "Custom URL New Tab",
  "version": "1.0",
  "description": "Extremely simple new tab extension that just renders the given page.",
  "homepage_url": "https://github.com/MrDiamondDog/simple-url-new-tab",
  "browser_specific_settings": {
    "gecko": {
      "id": "urlnewtab@example.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "action": {
    "default_title": "New Tab Options",
    "default_popup": "options.html"
  },
  "permissions": [
    "storage",
    "scripting"
  ],
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "chrome_url_overrides": {
    "newtab": "newtab.html"
  }
}