Examine source code of YT-Levelr

{
  "manifest_version": 3,
  "name": "YT Levelr",
  "version": "1.3.5",
  "description": "Automatic loudness levelling for YouTube — useful for podcasts",
  "homepage_url": "https://github.com/AndyP2/yt-levelr",
  "browser_specific_settings": {
    "gecko": {
      "id": "yt-levelr@apmicro",
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    }
  },
  "permissions": [
    "storage",
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "action": {
    "default_popup": "popup.html",
    "default_title": "YT Levelr"
  },
  "icons": {
    "48": "icons/icon48.png",
    "96": "icons/icon96.png",
    "128": "icons/icon128.png"
  }
}