Comment 9 for bug 387957

This is not an obvious usability flaw, and may even be considered a feature as-is. The behavior is similar on Mac OS -- typing while browsing the Save dialog jumps to files and folders whose names begin with the letters typed. This enabled advanced users to quickly jump to their targets in dense directories. Changing this behavior would be seen as a serious regression by many, so it needs a user testing and thorough interaction analysis. Therefore, it's not a paper cut.