Examine source code of Close Window Button

{
  "manifest_version": 3,
  "name": "Close",
  "version": "3.0",
  "description": "Close",
  "permissions": [],
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "close@dhanush.com",
      "strict_min_version": "109.0"
    }
  }
}