Examine source code of Page Load Sound

{
  "manifest_version": 2,
  "name": "Page Load Sound",
  "version": "1.0",
  "description": "Play a short sound when a page finishes loading.",
  "icons": {
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_script.js"
      ],
      "run_at": "document_end"
    }
  ],
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{858a8222-f5d2-42c7-8484-e968deb57596}"
    }
  }
}