Examine source code of Gmail Shortcuts Plus

{
  "manifest_version": 3,
  "name": "Gmail Shortcuts Plus",
  "version": "1.0.0",
  "description": "Use shortcuts to move between previous and next email in Gmail.",
  "browser_specific_settings": {
    "gecko": {
      "id": "gmail-shortcuts-plus@gaurav.local",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "permissions": [
    "storage"
  ],
  "action": {
    "default_title": "Gmail Shortcuts Plus",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://mail.google.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "48": "icon48.png",
    "128": "icon128.png"
  }
}