Examine source code of cash calculator

{
  "manifest_version": 2,
  "name": "cash calculator",
  "version": "1.0",
  "description": "just type how much money you have after given round.",
  "content_scripts": [
    {
      "matches": [
        "*://topper64.co.uk/nk/btd6/rounds/regular"
      ],
      "js": [
        "script.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{b3ba6bec-0194-4cc7-9854-dff6be10243e}"
    }
  }
}