Examine source code of Shirt Sizer

{
  "manifest_version": 3,
  "name": "Shirt Sizer",
  "version": "1.0",
  "description": "Convert shirt sizes for men, women, and children across US, EU, UK, JP, AU, and CN systems.",
  "permissions": [],
  "action": {
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "shirt_sizer@benes.iwp.edu"
    }
  }
}