I frequently find that some of the window previews in the Windows 7 taskbar will be lost, especially after a window has been minimized or hidden for a considerable period of time. Instead of the normal preview of the window I just see a gray box with the program icon in it.
This is a pain when I have a dozen Firefox windows open and can no longer quickly distinguish windows in the preview. Is there anything I can do to alleviate this? Any way to tell windows to keep around the previews longer or some key combo that will refresh all of the previews?