It occurred to me that this might have happened in one of my spacier frames of "mind" that the pop-up could have been left over from a link I opened in a new window, but I didn't notice it until I started shutting windows prior to logging off.

I haven't seen it since.  Sorry about the false alarm.

I've been tempted to install one of the programs at Tucows that eliminates popups, but I've been afraid that it would also prevent links from opening which were intended to open in a new window through javascript.  Many provider websites use that for displaying images.  A couple of sites (not provider sites - more fine art and, oddly enough, travel sites) are set to disable right click for copyright purposes so I would rather not throw the baby out with the bathwater.  Any recommendations?