In June 2025, Pierov contributed to mozilla/gecko-dev by implementing privacy-preserving font substitution for Windows under the Resist Fingerprinting (RFP) initiative. Using C++ and the Windows API, Pierov introduced a hardcoded FontSubstitutes list that activates when RFP is enabled, ensuring font list initialization consistently applies these substitutions. This approach prevents locale leakage through font enumeration, thereby enhancing user privacy while maintaining reliable font rendering. The work focused on font rendering and privacy, aligning with cross-platform consistency goals. Although the contribution was limited to a single feature over one month, it addressed a nuanced privacy concern with targeted, maintainable engineering.