This will help some people who have complained about some of the YouTube Videos locking up there browser and giving them Unresponsive Script Errors.
Currently some versions of Firefox are having issues with HTML5 video streams. If you are signed into a Google account/youtube in order to fix this problem go on the HTML5 page ( http://www.youtube.com/html5 ) at the bottom of the page, you will see “You are currently in the HTML5 trial.” and “Leave the HTML5 Trial”. Click on the second option and you will get rid of this error.
This may help other browsers also from the script message.