My Firefox froze up with a message purporting to be from the FBI

I’ve not started to diagnose this yet. I hit “Esc” key and got a message from the FBI informing me that I had to got to K-Mart, Walgreens or 7-11 and pay a $200 fine within the next 72 hours.

The message is full screen and I cannot even get out to run anti-malware utilities.

This is MPSIMS isn’t it?

And it’s also a scam. Don’t do it.

Hulpful page:

Maybe a dumb question, but does alt-F4 make it go away?