Examine source code of InboxToKindle

{
  "manifest_version": 2,
  "name": "InboxToKindle",
  "version": "1.0.0",
  "description": "Send web articles to your Kindle or Boox e-reader",
  "permissions": [
    "activeTab",
    "tabs",
    "storage",
    "https://inboxtokindle.com/*",
    "https://substacktokindle.com/*"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "lib/Readability.js",
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "extension@inboxtokindle.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": [
          "technicalAndInteraction"
        ]
      }
    }
  }
}