"Quit.warning" FF bug is quite old, I don't know why it still not fixed. As for YouTube-Freeze "feature" which was found about a year ago, here're my last tests: it works fine with last official XP version (26.5.0 Atom/WinXp, vp8/vorbis 360p) and Feodor2's mod v27.2.0a1 + LAV-splitter (vp9/opus 720p). Also, Feodor2 wrote that there're no freezings in Windows 7.