Firefox youtube video problem; Why is there a green line in my youtube videos?

I use Facebook in Chrome / Firefox, and recently I tried playing a YouTube video that someone posted on their wall. The static image of the video (that you see before you click the play button) looked fine. But when I clicked the play button, the video playback area was split across the center by a green horizontal line, and there were two, squashed, duplicates of the video playing above and below the line.

I thought it might be a Facebook issue, so I opened the same video up on the YouTube site, but with the same results.
I am writing how i just solve the problem

• So I tried it in IE8 and it worked just fine. 
• I figured the problem might be an outdated version of the Flash player for Chrome, so I updated the Flash player, making sure that I selected the "other browsers" version of the player, but the problem was still there.
• I just uninstall the browser and againg re-install it but there i found the same problem
• I just update the display driver of my computer and restart the computer but this time also i faced the same problem.
• lastly i just get helped from my friend and as he said just to disable the hardware acceleration of the flash player itself so i just did the same and i worked fine... I dont know why it doesnot work with hardware acceleration..but it resolved anyway...