The Great YouTube Blackout Spreads

I was over at my mother’s house for our family’s annual Summer Turkey Day, and it turns out that she can no longer play YouTube videos on her computer. This is the damnedest problem. It’s the exact same thing that happened to me a few weeks ago. In my case, I can’t play them on Opera, so I have to open Firefox whenever I want to watch a YouTube video. In her case, she can’t play them on Firefox, so she has to open IE to watch them. I reinstalled Flash and updated Firefox while I was over, but it didn’t do any good — just as it didn’t do me any good when I did the same thing on my machine.

I just can’t figure this out. Is it some kind of weird malware? But that doesn’t even make sense. What kind of malware would dick around with YouTube, but only on your primary browser? Is it possibly related to antivirus software? I’m completely stumped. Has anyone else encountered the same thing? Or is this literally a problem restricted to members of the Drum family?