Examine source code of YouTube To Mp3 Button

{
  "manifest_version": 2,
  "name": "YouTube To Mp3 Button",
  "version": "2.0",
  "homepage_url": "https://x2download.com",
  "description": "Free YouTube to Mp3 Button allows you to save YouTube video and mp3 files just in 1 click",
  "icons": {
    "32": "icons/icon-32.png",
    "96": "icons/icon-96.png"
  },
  "permissions": [
    "https://x2download.com/download-youtube-to-mp3",
    "https://x2download.com/download-video-facebook",
    "https://x2download.com",
    "webRequest",
    "<all_urls>"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*",
        "*://youtube.com/*",
        "*://youtu.be/*"
      ],
      "js": [
        "main.js"
      ],
      "run_at": "document_idle"
    }
  ]
}