A reader visiting our page on Facebook encountered the popup window shown above. When we surfed the site looking for similar versions of mutual friends on other pages and profiles, we didn’t find anything.

So we’ve asked Facebook spokespeople whether the screenshot shown above is test run by the site itself or the work of a third party. We’ll update this post with whatever we find out.

And perhaps you, dear readers, can help fill in the blanks here: Have you seen popup windows showing photos of mutual friends, either on Facebook pages or profiles?

Props to Zoltán Faludi for the tip and screenshot.