Examine source code of Custom Tab

{
  "manifest_version": 2,
  "name": "Custom Tab",
  "version": "1.1",
  "description": "Modifies the Appeareance of new Tabs",
  "chrome_url_overrides": {
    "newtab": "web/index.html"
  },
  "icons": {
    "48": "icons/home-48.png"
  },
  "options_ui": {
    "page": "web/options/options.html",
    "browser_style": true
  },
  "permissions": [
    "storage",
    "theme"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "customtab@tobi1805"
    }
  }
}