Recently Firefox 3 moved away from having separate back and forward history dropdowns and replaced them with a single combined history. At first, this seemed to be very strange, but after using it for a day I loved it: it's much easier to use, as you don't have to keep track of two histories, which makes finding the correct site easier.

If people feel strong about keeping the old separated history, an option would be to provide the combined history navigation element "<- -> \/" in addition to the current back "<- \/" and forward "-> \/" elements in the toolbar editor.