Well Guys
I couldn't wait so I uninstalled security update KB975561, the good news is that I now have Firefox back and it now works as it did before.
The bad news is that my Opera browser still does not play YouTube videos, I can only guess that this update changed something and uninstalling did not put that totally right.
Blackhorse 70V
I just check the Opera site and there is no V10.5, unless there is beta version your thinking of.
So, to get back to where I was before I will have to wait for an Opera update, I can always use FF or IE to play YouTube videos.
UK Bob
PS. Sorry Blackhorse 70V, I gotta eat some humble pie
Opera 10.5 exist, but in my own defence my Opera 10.10 says there are no upgrades available and this morning I could not quickly find any reference to 10.5. However, this lunchtime, I've just seen it and will check it out when I get home.