Examine source code of YouTube Player Enhancer

{
  "manifest_version": 3,
  "name": "YouTube Player Enhancer",
  "version": "1.0.0",
  "description": "VLC-like seekbar that stays hidden during keyboard shortcuts, plus force 16:9 with a custom vertical-stretch slider — for YouTube.",
  "permissions": [
    "storage",
    "activeTab"
  ],
  "host_permissions": [
    "*://*.youtube.com/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "ype@youtube-player-enhancer",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    },
    "gecko_android": {
      "strict_min_version": "142.0"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "css": [
        "content.css"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start",
      "all_frames": false
    }
  ],
  "action": {
    "default_popup": "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"
  },
  "web_accessible_resources": [
    {
      "resources": [
        "icons/*"
      ],
      "matches": [
        "*://*.youtube.com/*"
      ]
    }
  ]
}