Examine source code of osu! koko

{
  "name": "osu! koko",
  "version": "2.6.5resigned1",
  "description": "osu! koko download beatmaps automatically! (Now working in old site!)",
  "author": "Jecsham",
  "manifest_version": 2,
  "icons": {
    "16": "img/icon16.png",
    "48": "img/icon48.png",
    "128": "img/icon128.png"
  },
  "browser_action": {
    "default_title": "Open osu! koko",
    "default_icon": "img/icon128.png",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "https://osu.ppy.sh/beatmapsets/*",
        "https://osu.ppy.sh/s/*",
        "https://osu.ppy.sh/b/*"
      ],
      "css": [
        "css/dom-style.css"
      ],
      "js": [
        "js/content.js"
      ]
    }
  ],
  "permissions": [
    "tabs",
    "storage",
    "https://osu-koko.herokuapp.com/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{05ad38c6-fffe-4096-8492-fbfae9ea1995}"
    }
  }
}