Developed the Dynamic Menu Item Management API for the thunderbird/tbpro-add-on repository, enabling dynamic creation, updating, and removal of menu items and submenus within the Thunderbird Pro application. The work focused on aligning the API design with the existing app-menu architecture to support extensibility and future partner integrations. Leveraging JavaScript and JSON, the implementation introduced experiment flag support to measure menu customization usage and impact. This feature established a flexible foundation for UI customization, allowing rapid iteration and business-oriented experiments, while also laying the groundwork for menu item persistence and maintainability in future expansions. No bug fixes were recorded.