You tube video juddering

Hi All, well something has happened to my youtube viewing. All the videos judder/shake but sound is ok. All videos in iPhoto or when I watch a film on Netflix plus when I download a video from youtube all works fine. I am using a mid 2011 iMac 2.7Gig Intel i5 running OSX 10.9.2, I have been running this s/w since it came out but this prob only started a few days ago - I have tried all I can think of (but I am a BOF) so any help/suggestions would be much appreciated.



Thanks

Mike

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