Examine source code of YT Playlist Length

{
  "manifest_version": 2,
  "name": "YT Playlist Length",
  "version": "1.0",
  "description": "It will Show the analytics of a Youtube Playlist",
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/playlist?*"
      ],
      "js": [
        "index.js"
      ]
    }
  ],
  "permissions": [
    "*://duckduckgo.com/html/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{7dc7305e-6726-4fc5-8aa3-65768f5f926c}"
    }
  }
}