Examine source code of My Public IP

{
  "manifest_version": 2,
  "name": "My Public IP",
  "description": "Displays your public IP address and the country that it belongs to.",
  "version": "1.43",
  "browser_action": {
    "default_popup": "index.html",
    "default_title": "My Public IP"
  },
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "permissions": [
    "http://ip-api.com/*"
  ],
  "web_accessible_resources": [
    "images/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{87333a02-936e-4c67-b9f8-453ccc2c9ec8}"
    }
  }
}