Examine source code of Gmail Thread Notes

{
  "manifest_version": 2,
  "name": "Gmail Thread Notes",
  "version": "1.0.5",
  "description": "Add private notes to Gmail threads. Notes appear above the subject line and sync across devices.",
  "permissions": [
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Gmail Thread Notes"
  },
  "content_scripts": [
    {
      "matches": [
        "https://mail.google.com/*"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "content.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "16": "icons/note-16.png",
    "48": "icons/note-48.png",
    "128": "icons/note-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "gmail-thread-notes@tj",
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    }
  }
}