High CPU usage when watching youtube videos (HTML5)?

This is something I had to deal with as well and I came to the conclusion if I use a desktop application like Miro, Totem, VLC, or MiniTube it makes my system run much better and cooler.

I prefer Miro, but it still needs some more development until it is perfect and crash free. I hear MiniTube is great, but it is a paid app. Totem works, but isn't as convenient.

I know this might not be your preferred method, but using Miro has opened up a lot of great content I wouldn't have found otherwise like free and creative commons audio books, music, and video series/episodes.

Also if you go this route check out Fluendo Codec. It improves video quality and works with Gstreamer. Only costs about $30 bucks.