I have tried "opting out of HTML5" but it just takes me to a page that shows what Safari browser is capable of playing. This is on macOS Sierra and the latest Safari version 10.0.3. I have also reset Safari (cleared history too) and nothing. I don't have any extensions installed. I have downloaded Adobe Flash Player, and have enabled it for youtube.com, but it never loads videos reliably, unlike my windows machine that plays videos and displays the thumbnails/comments perfectly. How do I get this working besides trying Chrome browser (trying to switch to Safari on MacOS)? I have searched on Google for longer than I feel like I should, and the countless threads/posts date back to early 2012, so this problem seems to be ongoing. Sometimes the videos will load, if I press the X button next to the address bar while a youtube video is loading, with no comments or thumbnails loaded, sometimes the video will play then, but what's the point if nothing else loads?