... PROBLEM SOLVED!!! ... I right clicked on You Tube's blank square (black or white) and clicked on "Report playback issue" ... I did and that took me to the following page:
... where I found an explanation about Adobe ... bla, bla, bla and the following:
"While we work with Adobe to smooth out these kinks, the following steps will allow you to disable hardware-accelerated playback: "
1 Right-click in the middle of the video below (or on the on the video you're having issues with)
2 Click Settings
3 Click the left-most tab
4 Uncheck the 'Enable hardware acceleration' checkbox to disable hardware acceleration.
5 Refresh the page