Today I noticed that Safari doesn't show anymore the videos shown on Youtube; I just see a black rectangle, and when I try to use the popup menu in that area, it doesn't appear.
As far as I can remember, one week ago I was able to see videos on Youtube. Something is changed in this week; for what I can remember, Safari has not been updated, in these days.
How can I find the reason of the problem, and eventually resolve it?