Examine source code of Minimal Date Countdown

{
  "manifest_version": 3,
  "name": "Minimal Countdown",
  "version": "1.0",
  "description": "A clean, minimalist countdown timer for your multiple events.",
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "minimal-countdown@yourdomain.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon.png",
      "48": "icon.png",
      "128": "icon.png"
    }
  }
}