Examine source code of Frequency Tuner

{
  "manifest_version": 3,
  "name": "Frequency Tuner",
  "version": "3.1",
  "description": "Ajusta a frequência do áudio para 432Hz, 528Hz ou normal (440Hz)",
  "browser_specific_settings": {
    "gecko": {
      "id": "frequency-tuner@freddev.local",
      "strict_min_version": "109.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_title": "Ajustar Frequência"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "icons": {
    "48": "icon-48.png",
    "128": "icon-128.png"
  }
}