Examine source code of Duplicate Tab Closer

{
  "manifest_version": 3,
  "name": "Duplicate Tab Closer",
  "version": "1.1.0",
  "description": "Counts duplicate tabs on the icon. Click to close older copies and keep the most recently used tab. Pinned-safe mode included.",
  "permissions": [
    "tabs",
    "storage"
  ],
  "background": {
    "service_worker": "background.js",
    "scripts": [
      "background.js"
    ]
  },
  "action": {
    "default_title": "Duplicate Tab Closer",
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "duplicate-tab-closer@local.extension",
      "strict_min_version": "115.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}