Hi,
I also reported this to mozilla bugzilla: 1192900 - firefox crashes when resizing the youtube html5 player (vdpau related)
In brief, firefox crashes every time when using libva-vdpau-driver and trying to resize the html5 player. This video works:
How To Change Your Grips | MTB Maintenance Tips - YouTube
nvidia-bug-report.log.gz (127 KB)
firefox-youtube.log (4 KB)
firefox-youtube-bt.log (6.86 KB)