Examine source code of Tab Volume Controller

{
  "manifest_version": 3,
  "name": "Tab Volume Controller",
  "version": "1.1",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "96": "volumeicon.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "crappey@github"
    }
  }
}