Comment 5 for bug 774331

To illustrate why this is a problem: I have four open firefox windows and a download dialog. When I click the firefox button to reach the overview all but the download window are indiscernible at first glance. Just getting back to where I was takes some effort. It'l become faster after you've found that the last window is always on the top left (which I have just now after experimenting to get a better understanding of the behaviour for the bug report), but I would consider that a bug in itself (because you always have to reorientate yourself between switching windows).
Of course if you're using the keyboard you could use [Esc].