Examine source code of Free Trial Guardian

{
  "manifest_version": 3,
  "name": "Free Trial Guardian",
  "short_name": "Trial Guardian",
  "version": "1.0.0",
  "description": "Never get silently charged again. Detects free-trial signups and reminds you before they convert to paid — entirely on-device, no account, no data leaves your browser.",
  "browser_specific_settings": {
    "gecko": {
      "id": "free-trial-guardian@loomwooddigital.com",
      "strict_min_version": "121.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "permissions": [
    "storage",
    "alarms",
    "notifications"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "service_worker": "background.js"
  },
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ]
}