Worked on the mozilla/gecko-dev repository to enhance build stability, code clarity, and test reliability for the CSS grid layout engine. Addressed a GCC build error in Tracks::ResolveIntrinsicSizeForNonSpanningItems by updating type declarations in C++, ensuring compatibility and reducing build failures. Improved maintainability by refactoring nsGridContainerFrame.cpp, removing redundant mozilla qualifiers for clearer code. Enhanced test robustness by refining configuration for CSS grid track sizing tests, enabling multi-pass verification and reducing timeouts. Leveraged skills in C++, debugging, and testing to deliver targeted improvements that resulted in more dependable builds and streamlined code, supporting ongoing development and quality assurance efforts.