Examine source code of X.com Time Limiter

{
  "manifest_version": 2,
  "name": "Time Limiter",
  "version": "1.0.1",
  "description": "Adds a timer and blocks the website when time runs out.",
  "icons": {
    "48": "icons/time-limiter.png"
  },
  "permissions": [
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.x.com/*"
      ],
      "js": [
        "time-limiter.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{8b8c1720-1862-4656-9935-006ea24f2f67}"
    }
  }
}