Examine source code of pure-youtube

{
  "manifest_version": 2,
  "name": "pure-youtube",
  "author": "Fedor Urvanov",
  "homepage_url": "https://urvanov.ru",
  "version": "1.2",
  "description": "Removes recomendations from youtube.com",
  "content_scripts": [
    {
      "matches": [
        "https://www.youtube.com/*"
      ],
      "css": [
        "pure-youtube.css"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{3451b5f2-eb3f-44e3-b962-fb930a891f2f}"
    }
  }
}