Examine source code of YouTube Layout Customizer

{
  "manifest_version": 3,
  "name": "YouTube List View (Custom)",
  "version": "1.0",
  "description": "Custom YouTube layout tweaks",
  "permissions": [
    "storage",
    "tabs"
  ],
  "host_permissions": [
    "*://*.youtube.com/feed/subscriptions"
  ],
  "action": {
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/feed/subscriptions"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "yt-list-view@custom",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}