Found it interesting today that an ad at the top of
www.Youtube.com for Samsung Galaxy was showing as a green rectangular window but yet the watermark etc shown as Galaxy, which I assume is Samsung Galaxy, and it was crashing Flash Plugin and causing Firefox to lock up. After about 20 seconds a message popped up giving choice to wait or shutdown the flash plugin that is not responding. Tried this 3 times on same computer, then gave up on my desktop and fired up my netbook and same issue happened with latest Firefox and Youtube main page's Galaxy ad crashing it.
Maybe when I go to Youtube later, they will have fixed or moved on to a different advertisement that doesnt crash Flash on Firefox and render Youtube non-functional, since without Flash youtube cant play videos etc. Did not test it with IE or any other browser.
Seems as though this ad is a corrupt file linked to their main site, or doesnt play well with latest Firefox and Flash Plugin.