Try to disable Hardware Acceleration.
Looks like the same problem as mentioned here

You should install the proprietary driver from your graphics card manufacturer and use that one instead of the default open-source (x.org).

AMD no more support graphic cards below hd5000 for linux.

Does disabling "Use hardware acceleration when available" in Settings help? You'll need to enable Advanced settings (bottom of the Browser page) to see it, then it'll be right above that.

It helps but make YouTube sucks when HD resolution used.