Examine source code of Page Fade Sound

{
  "manifest_version": 2,
  "name": "Page Fade Sound",
  "version": "1.0",
  "description": "Trang tải xong phát âm thanh fade-in ngắn; khi đóng tab phát fade-out ngắn.",
  "permissions": [
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{822edf90-4ff3-430c-af68-21f94b9b06ed}"
    }
  }
}