This was introduced some weeks ago. I'm not sure whether this is a dup, could not find anything. Happens on OS/2 and on Win98 (confirmed by another user) so seems to be an XP bug. You can see this by closing a browser frame window. It will hide and then an empty frame with with titlebar will reappear with the same size/position which then completely disappears.
I occasionally see something like this on linux, often when closing a popup. Another window of the same size pops up, and as soon as I place it disappears along with the popup.
This is OS/2 specific, reassigning to me.
Created attachment 30398 [details] [diff] [review] don't show the window on each WM_FOCUSCHANGE, basically back out 1.37 change
the patch has the problem of breaking 56770 again. We need WM_ACTIVATE as well to get proper keyboard input focus. However, the original fix has the problems mentioned. We might have to introduce some mIsBeingClosed flag to nsWindow and set that in the XP code that does the window->Show(PR_FALSE) before closing it. Any other suggestions?
This will be fixed by the focus checkin in 145561 *** This bug has been marked as a duplicate of 145561 ***