Examine source code of Youtube MrBeastify

{
  "manifest_version": 2,
  "name": "YouTube MrBeastify",
  "version": "1.9.0",
  "icons": {
    "96": "icon.png"
  },
  "description": "Modify YouTube thumbnails to include MrBeast",
  "browser_action": {
    "default_popup": "settings.html"
  },
  "permissions": [
    "storage",
    "*://*.youtube.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "mrbeastify.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "web_accessible_resources": [
    "images/*.png",
    "images/*.json"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{169e0f20-b4d6-4670-a852-e78a56f68264}"
    }
  }
}