Examine source code of YT loop button

{
  "manifest_version": 2,
  "name": "YT loop button",
  "short_name": "YouTube repeat button",
  "version": "1.0",
  "description": "Add a repeat/loop button to loop every YouTube videos you watch.",
  "icons": {
    "128": "icons/icon_128.png"
  },
  "page_action": {
    "default_icon": "icons/icon.png",
    "default_title": "YouTube loop button"
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.youtube.com/*",
        "http://www.youtube.com/*"
      ],
      "js": [
        "injector.js",
        "lib/jquery-3.3.1.js"
      ]
    }
  ],
  "applications": {
    "gecko": {
      "id": "@ylb",
      "strict_min_version": "57.0"
    }
  },
  "permissions": [
    "tabs"
  ]
}