During June 2025, this developer expanded test coverage for CSS marker animations in the mozilla/gecko-dev repository, focusing on the ::marker pseudo-element and its animation-related properties. They authored Web Platform Tests in HTML to validate parsing and computed values for animation-range, animation-range-start, animation-range-end, and animation-timeline, ensuring robust regression safety and improved cross-browser compatibility. Their approach emphasized traceability by linking work to relevant bugs and pull requests, supporting alignment with WebKit. By concentrating on web platform testing rather than bug fixes, they enabled earlier detection of regressions and contributed to safer, more reliable shipping of CSS animation features.