Examine source code of Web Interface Customizer

{
  "manifest_version": 3,
  "name": "Web Interface Customizer",
  "version": "1.0",
  "description": "Customize the appearance of websites by injecting custom CSS.",
  "permissions": [
    "storage",
    "scripting"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "action": {
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "web_customizer@example.com",
      "strict_min_version": "109.0"
    }
  }
}