I was playing around with a couple of FireFox extentions that add some interesting thumbnailing capabilities to the browser and it reminded me of a sketch I made of adding rich thumbnail capabilities into the browser back button.
The idea was to show richer previews when opening the "split-button" section of the browser back button. I had another similar design that showed your navigation history as a film-strip across the top of the browser as well. Both designs looked to make the browser more of a visual tool by helping you identify pages visually rather then just by their text descriptions.