Examine source code of KindleFlow

{
  "manifest_version": 3,
  "name": "KindleFlow",
  "version": "0.1.0",
  "description": "Send the rendered article page you can read in your browser to KindleFlow.",
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "permissions": [
    "activeTab",
    "scripting",
    "storage"
  ],
  "host_permissions": [
    "https://substack.com/*",
    "https://*.substack.com/*",
    "https://kindleflow.tail217062.ts.net/*"
  ],
  "optional_host_permissions": [
    "http://*/*",
    "https://*/*"
  ],
  "action": {
    "default_title": "Send to KindleFlow",
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon-16.png",
      "32": "icons/icon-32.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "kindleflow-extension@tjegbejimba.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}