Examine source code of Add a Download button on YouTube

{
  "manifest_version": 2,
  "name": "YouTube Downloader Button",
  "version": "1.0.13",
  "description": "This extension allows you to download sounds or videos directly from YouTube.",
  "browser_specific_settings": {
    "gecko": {
      "id": "{5d0ef29c-9413-4e33-b1fa-a168d07b9c53}",
      "data_collection_permissions": {
        "required": [
          "websiteContent"
        ]
      }
    }
  },
  "icons": {
    "32": "icons/icon-32.png",
    "96": "icons/icon-96.png"
  },
  "permissions": [
    "activeTab",
    "tabs",
    "*://*.youtube.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*",
        "*://youtube.com/*",
        "*://youtu.be/*"
      ],
      "js": [
        "main.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_action": {
    "browser_style": true,
    "default_icon": {
      "32": "icons/icon-32.png",
      "96": "icons/icon-96.png"
    },
    "default_title": "YouTube Downloader Button",
    "default_popup": "popup/popup.html"
  }
}