Examine source code of Mono Audio Mixdown

{
  "manifest_version": 3,
  "name": "Mono Audio Mixdown",
  "version": "1.0.0",
  "description": "Forces stereo audio to mono so single-channel ('broken') audio plays in both ears. Per-site toggle + global default.",
  "permissions": [
    "storage"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_title": "Mono Audio Mixdown",
    "default_icon": {
      "48": "icon.png",
      "128": "icon.png"
    }
  },
  "icons": {
    "48": "icon.png",
    "128": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "mono-mixdown@local",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}