Examine source code of Librus Enhancer

{
  "manifest_version": 2,
  "name": "Librus Enhancer",
  "version": "1.2.2",
  "description": "Sprawia, że Librus jest trochę mniej antyludzki.",
  "icons": {
    "48": "icons/icon_48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://portal.librus.pl/*",
        "https://synergia.librus.pl/*",
        "https://www.librus.pl/*"
      ],
      "js": [
        "jquery.slim.min.js",
        "browser-polyfill.min.js",
        "contentscript_common.js",
        "contentscript.js"
      ],
      "run_at": "document_end",
      "all_frames": true
    },
    {
      "matches": [
        "https://api.librus.pl/OAuth/Authorization*"
      ],
      "css": [
        "login_iframe.css"
      ],
      "js": [
        "jquery.slim.min.js",
        "browser-polyfill.min.js",
        "contentscript_common.js",
        "contentscript_login_iframe.js"
      ],
      "run_at": "document_idle",
      "all_frames": true
    }
  ],
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "storage",
    "https://portal.librus.pl/*",
    "https://synergia.librus.pl/*",
    "https://www.librus.pl/*",
    "https://api.librus.pl/*",
    "https://liblink.pl/*"
  ],
  "background": {
    "scripts": [
      "browser-polyfill.min.js",
      "background.js"
    ]
  }
}