Examine source code of Closer Menu

{
  "manifest_version": 3,
  "name": "Tab Closer Menu",
  "version": "1.2.1",
  "description": "Close Firefox tabs and other Firefox windows",
  "permissions": [
    "tabs"
  ],
  "update_url": "https://seninsiten.com/updates.json",
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "tabclosermenu@example.com"
    }
  }
}