Examine source code of Recently Closed

{
  "manifest_version": 3,
  "name": "Recently Closed",
  "version": "1.0.0",
  "description": "Merges Recently Closed Tabs and Recently Closed Windows into one list. Shows the 5 most recent inline (with subtab counts for windows) and the rest under \"See all\".",
  "browser_specific_settings": {
    "gecko": {
      "id": "recently-closed@jithomas.mozilla.com",
      "strict_min_version": "115.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "permissions": [
    "sessions",
    "tabs"
  ],
  "action": {
    "default_title": "Recently Closed",
    "default_popup": "popup/popup.html",
    "default_icon": {
      "16": "icons/icon.svg",
      "32": "icons/icon.svg"
    }
  },
  "icons": {
    "48": "icons/icon.svg",
    "96": "icons/icon.svg"
  }
}