You can expand each section with implementation details, experimental results, and references. Abstract Selenium Grid enables distributed test execution across multiple browsers and platforms. However, its native capabilities lack extensibility for custom reporting, dynamic node management, authentication, and advanced load balancing. This paper presents a plugin-based architecture for Selenium Grid 4, allowing third-party plugins to inject custom logic at key lifecycle events. We implement a reference plugin that adds real-time test monitoring, dynamic node provisioning via Docker, and a custom dashboard. Evaluation shows minimal performance overhead (≤8%) and significant improvements in scalability and observability.