Examine source code of ShippingCalculator

{
  "manifest_version": 2,
  "name": "ShippingCalculator",
  "version": "1.0",
  "description": "Estimate shipping costs based on weight and destination.",
  "permissions": [
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{cc5657cf-fee0-4757-8f9b-cb3ed9a8050a}"
    }
  }
}