Examine source code of Hello Popup

{
  "manifest_version": 3,
  "name": "Hello Popup",
  "version": "1.0",
  "description": "Shows a Hello World popup when you click the toolbar icon.",
  "action": {
    "default_title": "Say Hello",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "hello-popup@example.com"
    }
  }
}