Worked on the mozilla/gecko-dev repository to address a critical issue affecting text selection within Shadow DOM contexts. Delivered a targeted fix by updating the DOMSelection::extend method to use the DOMSelection anchor rather than the shadow-adjusted anchor, ensuring consistent selection behavior across editing and interaction methods in line with web standards. Validated the solution using Web Platform Testing and JavaScript, with changes linked to WPT PR 53246. This work improved the reliability of text editing in complex DOM scenarios, reduced cross-browser inconsistencies, and minimized developer debugging time, ultimately enhancing the user experience for applications leveraging Shadow DOM features.