Examine source code of DubPlus

{
  "manifest_version": 3,
  "version": "4.1.3",
  "name": "DubPlus",
  "short_name": "Dub+",
  "author": "Dub+ Devs",
  "description": "Dub+ - A Dubtrack.fm and QueUp.net script/extension for added features and customizations",
  "homepage_url": "https://dub.plus/",
  "action": {
    "default_icon": {
      "16": "icons/18.png",
      "32": "icons/32.png",
      "48": "icons/48.png"
    }
  },
  "content_scripts": [
    {
      "js": [
        "register-dubplus.js"
      ],
      "matches": [
        "*://*.dubtrack.fm/join/*",
        "*://*.queup.net/join/*"
      ],
      "run_at": "document_start",
      "world": "MAIN"
    },
    {
      "js": [
        "dist/dubplus.js"
      ],
      "css": [
        "dist/dubplus.css"
      ],
      "matches": [
        "*://*.dubtrack.fm/join/*",
        "*://*.queup.net/join/*"
      ],
      "run_at": "document_end",
      "world": "MAIN"
    }
  ],
  "icons": {
    "18": "icons/18.png",
    "19": "icons/19.png",
    "32": "icons/32.png",
    "48": "icons/48.png",
    "96": "icons/96.png",
    "128": "icons/128.png"
  },
  "host_permissions": [
    "*://*.dubtrack.fm/*",
    "*://*.queup.net/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{00319163-9639-49e6-ac0f-7d1fb989707d}",
      "strict_min_version": "109.0"
    },
    "safari": {
      "strict_min_version": "14"
    }
  }
}