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youtube error msg & html5

Does anyone know what to do abouut this error messagfe on YouTube.....???

Your browser does not currently recognize any of the video formats available

Thanks.   I've searched for the answer but nothing makes any sense.... and many of the answers are very old....  The youtube screen points me to a page about firefox and html5 but I can't find out how to fix the problem......

It's nuts...  Thanks in advance...