I'm on 10.11 GM, and I've noticed that for a while now Safari has been have issues in loading YouTube & Google mainly, but also with some other HTML5 websites. The main issue is with loading the pages. When I open a YouTube page, sometimes it loads fully "in less than a sec." except for a few images, and it stays like so for a while. Sometimes it doesn't load at all "just a white page waiting to load forever". Sometimes the button wouldn't work. Refreshing the page sometimes work, sometimes doesn't. Anyone got any idea on how to fix this? I got fiber internet with a speed of around 30 Mbps down, 5 up.. Chrome & FF do not have any issues.. And I've tried turning off all of the extensions with not luck.. Solution: For anyone interested, it turned out that turning IPv6 off solves the issue..