У вашего броузера проблема в совместимости с HTML5
Just got through the Vorkath fight during the new Dragon Slayer 2 quest. It's not easy at first, but once you get the hang of it, it's really not too bad. Always keep protect from MAGE on, and make sure to keep moving! The easiest way to get killed, is to get caught in one spot for too long. Keep trying and you can do it! I hope this helps!
Link for Killing Galvek Guide - https://www.youtube.com/watch?v=cVA7qWH5mjI