Examine source code of YouTube Speed Master

{
  "manifest_version": 3,
  "name": "YouTube Speed Master",
  "version": "1.2",
  "description": "A control panel with a slider to adjust YouTube video speed, which auto-hides when not in use. Can also use + and -",
  "icons": {
    "16": "icon16.png",
    "32": "icon32.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "tsanevpeeter@gmail.com"
    }
  }
}