OK, got it again clicking a subscription link in my email to the MPGuino Workspace thread. I didn't even make it to the thread - Firefox just minimized itself as soon as the page started to load, and the popup replaced it. Here's the first dialog that pops up:
Then clicking OK gives you this:
Clicking OK here or Cancel in the first popup brings you here (spaces inserted to avoid inadvertent click):
http :// windows-defense . com /2009/1/_freescan.php?aid=77024209