Examine source code of YT Custom Speed Button

{
  "manifest_version": 3,
  "name": "YT Custom Speed Button",
  "version": "1.3",
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "description": "Adds a customizable multi-row playback speed menu to the YouTube video player.",
  "permissions": [
    "storage"
  ],
  "host_permissions": [
    "https://www.youtube.com/*"
  ],
  "action": {
    "default_icon": {
      "16": "icons/icon16.png",
      "32": "icons/icon32.png",
      "48": "icons/icon48.png"
    },
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.youtube.com/*"
      ],
      "css": [
        "content.css"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "ytcustomspeedbutton@addon.local",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}