Examine source code of 3xYouTube

{
  "manifest_version": 2,
  "name": "3xYouTube",
  "version": "1.0",
  "description": "Increase YouTube playback speed beyond 2x",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "host_permissions": [
    "*://www.youtube.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_action": {
    "default_popup": "menu.html",
    "default_icon": "icons/3xyt.png"
  },
  "icons": {
    "16": "icons/3xyt.png",
    "48": "icons/3xyt.png",
    "128": "icons/3xyt.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "3xyoutube@ipflux.io",
      "strict_min_version": "109.0"
    }
  }
}