Examine source code of Fallen London Sheetifier

{
  "manifest_version": 3,
  "name": "Fallen London Sheetifier",
  "version": "1.0.1",
  "description": "Adds a button to the browser game Fallen London that lets you save your character data to a CSV file.",
  "icons": {
    "16": "images/icon16.png",
    "32": "images/icon32.png",
    "48": "images/icon48.png",
    "96": "images/icon96.png",
    "128": "images/icon128.png"
  },
  "permissions": [],
  "content_scripts": [
    {
      "matches": [
        "https://www.fallenlondon.com/*"
      ],
      "js": [
        "sheetifier.js"
      ],
      "run_at": "document_start"
    },
    {
      "matches": [
        "https://www.fallenlondon.com/*"
      ],
      "js": [
        "interceptor.js"
      ],
      "run_at": "document_start",
      "world": "MAIN"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "sheetifier@flextension",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}