Strange split-second pop-up window in Mountain Lion

Question

I have a 2011 MBP 13 and I installed ML on Day one of launch. It's been perfectly fine ever since and I even think that the battery is slightly better.
However, while using the laptop, sometimes, for a split second a window, about 80% the size of the desktop screen appears and disappears, as though a pop-up window opened because I did something. However whenever it happens, I'm usually on sites like Facebook and BBC which don't have such pop-ups.
The pop-up window is always the same size and disappears before I can get a good look at it. I always check to see if it's minimized somewhere like a pop-up windows should but there is no sign of it. It started the day I got ML.
Any ideas?
I'm also had 2-3 hangs with ML, something I never had with Lion. Had to do a hard re-start.
Thanks

Answer 1

Thanks Clinton my question was more directed at the people who are having the popup because i was wondering if it was due to a specific setup of said CS6.
Another thing to consider to the users who are experiencing the random popup, in prefs > users > login items ... is there anything with a "!" sign next to it on start up? I say this because i found an old program in there which has since been uninstalled (stupidly i removed it before i wrote it down) but it was a time management program to monitor what you do when you're supposed to be working.
Any takers!?