Examine source code of Send2Kindle

{
  "name": "Send2Kindle",
  "version": "1.0.0",
  "description": "Send web content to your Kindle device",
  "manifest_version": 3,
  "author": "Confidence Okoghenun",
  "homepage_url": "https://send2kindle.confidence.sh",
  "action": {
    "default_popup": "index.html",
    "default_title": "Send Now"
  },
  "icons": {
    "16": "images/icon-16.png",
    "32": "images/icon-32.png",
    "48": "images/icon-48.png",
    "128": "images/icon-128.png"
  },
  "permissions": [
    "tabs"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{4c33b41e-83a0-43d4-ab62-393e8f69fe5b}"
    }
  }
}