To those running Sierra or High Sierra, and Safari, did you know you can pop a YouTube video out into a new window, so you can continue to see and listen while you go on browsing. Right click on the video, move your cursor over slightly and right click again. The second menu you see offers "Enter Picture in Picture". Do the same thing again (on the original video tab) and select "Exit Picture in Picture", or just close the tab. The PIP window will sit in one of the four corners of your screen, just move it where you want. It is a small window and it rides on top of your other windows.