pixeling with flash

The image bellow is an example of a problem that I've been experiencing recently.
Playing flash videos on Firefox has been terrible. In many cases Firefox has frozen and I've had to force terminate the flash-plugin and reload the page. removing and re-installing flash seemed to help a bit. In a last attempt I've switched to Chrome which I find a bit ugly and lacking in terms of plugins in comparison to Firefox. On the plus side it feels much faster. With either I will get scores from speed test in the range of 54-52Mbps. This screen shot bellow if from watching youtube on chrome.

It always appears as a block of flickering black pixels. Any suggestions?
I will eventually reformat my computer and switch to windows 10 but I don't really want to do a reformat before switching.