Examine source code of Mobile Website Tester

{
  "browser_action": {
    "browser_style": true,
    "default_title": "Mobile Website Tester",
    "default_popup": "window.html",
    "default_icon": {
      "64": "icons/logo_64.png"
    }
  },
  "icons": {
    "32": "icons/logo_32.png",
    "64": "icons/logo_64.png",
    "128": "icons/logo_128.png"
  },
  "description": "Test website responsiveness for mobile view.",
  "manifest_version": 3,
  "name": "Mobile Website Tester",
  "version": "1.0",
  "browser_specific_settings": {
    "gecko": {
      "id": "mobile-website-tester11@unique.extension.id"
    }
  }
}