Examine source code of Wplace Timer

{
  "manifest_version": 2,
  "name": "Wplace Timer",
  "version": "1.0",
  "description": "A timer to inform you when your charges have replenished on wplace.live",
  "permissions": [
    "alarms",
    "storage",
    "notifications"
  ],
  "background": {
    "scripts": [
      "wplace_timer.js"
    ],
    "persistent": true
  },
  "content_scripts": [
    {
      "matches": [
        "*://wplace.live/*"
      ],
      "js": [
        "update_timer.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "48": "icons/favicon-1.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{68ff0db5-4f5a-436f-a2eb-68872401606c}"
    }
  }
}