Following a suggestion from someone else I changed my display to 16 bit high colour instead of 32 bit true colour. I think this has solved the problem, but I'm not totally 100% sure which is why I haven't posted this yet. But I think it has worked. you
need to restart your computer after making the change too.
One thing I do know is that it definitely only happens on the internet and usually when I'm trying to watch a video - BBC news website.
I am thinking that if the colour settings change is the answer and as I know it is internet mostly video, Firefox as well as IE, linked that it may be something to do with a video plug in.
Good luck.