The Vonage Video Express extension for Firebase is a tool that helps developers quickly create multiparty video conferencing applications using the Vonage Video API. The extension provides an easy-to-use interface for integrating video chat into existing Firebase projects, abstracting away low-level details such as credentials management and applying optimizations to improve performance. By installing the extension, developers can leverage the power of Vonage's cloud-based video platform within their Firebase applications, enabling seamless video conferencing capabilities with minimal setup and configuration.