HJT / Blank Window Pops Up But Disappears In The Taskbar

I've been having this issue where while I'm surfing the internet using Firefox, a blank window pops up and then disappears in the taskbar on the bottom. It's too quick to grab and find. I checked my running processes, nothing out of the ordinary. I ran a full blown virus scan with Norton AV Corporate, with all updates. I have ran Adware. with newest updates smart and full scan, PestPatrol (with newest updates), Aluria. And none of these has found anything. I even went into IE and Firefox and double-checked my plugins to make sure there are no strange plug ins which may have been spawning a process, and there is nothing out of the ordinary.