In September 2021, Fabien Stz worked on the thunderbird/thunderbird-android repository, developing a user-facing feature that allows users to select their preferred email content type display. He implemented a UI menu option enabling switching between plain text and HTML rendering, and introduced a global display setting to persist this preference across sessions. Using Java and Kotlin, Fabien updated the message rendering logic to honor the selected format, ensuring the view updates dynamically. Drawing on Android development and UI/UX design skills, his work improved readability and customization, addressing user needs for flexible content viewing without introducing bug fixes during this period.