Examine source code of Facebook UI Cleaner

{
  "manifest_version": 3,
  "name": "Facebook UI Cleaner",
  "version": "1.0",
  "description": "Hides the left and right panels to make the user interface 'cleaner'",
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://www.facebook.com/*"
      ],
      "css": [
        "content.css"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "your-unique-id@beeg.com",
      "strict_min_version": "91.0"
    }
  }
}