Ath - well, when you say "connector" do you mean Adobe flash? Thing is that it is a firefox plugin.
AND the machines are running MS Security Essentials.
@Miles - it does look similar. The browser isn't crashing, and switching tabs doesn't work either.
It's rather painful, too. You just can't watch. You have to watch and move the mouse.
Actually, I just noticed something else. This one computer was running Firefox 34, so I upgraded it to 35 via the help menu. And I was watching the progress meter and noticed that unless I moved the mouse, the little spinner in the upgrade panel would not move. Strange!
I'm going to run a memory test and see if it is a RAM issue.