I’ve been enormously frustrated with the way YouTube works on the Mac, links aren’t clickable & to get anything happening you need to right-click (or control-click) a link to open in a new tab or window. I have found an app in the MAS that fixes the problem. https://itunes.apple.com/au/app/deskapp-for-youtube/id1180531112
Navigation is simple & logical, when you click a link it opens in the app, when right-clicking a link to open in a new window, the video opens in your default browser. This works for me because I have a Safari extension to download videos.