Examine source code of Does Amazon Ship to ...?

{
  "manifest_version": 2,
  "name": "Does Amazon Ship to ...?",
  "version": "6.1.8",
  "description": "Button to check if Amazon items could be shipped to your country. The button appears on Amazon product page only.",
  "icons": {
    "48": "assets/icon.png",
    "128": "assets/icon_128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.amazon.com/*",
        "*://*.amazon.co.uk/*",
        "*://*.amazon.fr/*",
        "*://*.amazon.de/*",
        "*://*.amazon.it/*",
        "*://*.amazon.es/*",
        "*://*.amazon.ca/*",
        "*://*.amazon.com.mx/*",
        "*://*.amazon.com.au/*",
        "*://*.aliexpress.com/*",
        "*://*.aliexpress.ru/*",
        "*://*.gearbest.com/*",
        "*://*.ebay.com/*"
      ],
      "js": [
        "assets/scripts.js"
      ],
      "run_at": "document_end",
      "all_frames": true
    }
  ],
  "content_security_policy": "script-src 'self'; object-src 'self'",
  "web_accessible_resources": [
    "app.js",
    "styles.bundle.css",
    "assets/error.icon.png",
    "assets/good.icon.png",
    "assets/jquery-3.2.1.min.js",
    "assets/loading.gif"
  ],
  "background": {
    "persistent": true,
    "scripts": [
      "assets/background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "DoesAmazonShipTo@usefulhelper.com"
    }
  }
}