Examine source code of YouTube Rapper Toolkit

{
  "manifest_version": 2,
  "name": "YouTube Rapper Toolkit",
  "version": "1.4.0",
  "description": "Sort Watch Later + loop any beat section + download MP3 — built for writing bars.",
  "permissions": [
    "http://127.0.0.1:3456/*",
    "downloads"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "youtube-wl-sorter@local",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    },
    "gecko_android": {
      "strict_min_version": "142.0"
    }
  }
}