An update around mid May caused some Youtube videos to fail.  When this
happens, loading the video stops, leaving only the dot going around a circle
showing.  This happens with Firefox, Seamonkey and Chromium browsers.  The
videos that fail play OK in Windows.  To verify the problem, I tried the videos
with a VirtualBox VM or a fresh 42.2 install.  The problem videos played.  I
then cloned the VM and ensured the videos played.  I then updated the clone to
the latest updates and now the videos fail.  The original non-updated VM still
continued to play the videos.  It appears the problem is related to the type of
codec used.  For example, videos with the vp9 codec play, but those with
avc1.4d400d now fail.

Here are 2 links, this one plays OK:
https://www.youtube.com/watch?v=Rzqq581Q3Us

But this one doesn't:
https://www.youtube.com/watch?v=t8tdmaEhMHE


Again, this problem occurred recently.  Videos that played a few weeks ago now
fail.