Firefox is not optimized for widescreen or dualscreen monitors leaving lots of empty space when surfing the Internet. Jonathon Weare came up with a solid way to change the layout of Firefox to suit the needs of widescreen monitors by moving several elements of Firefox to different positions.
His first idea was to move the bar with all the tabs from the top location into the sidebar which adds two benefits. The first benefit is that the space on the sides is used to store elements that are needed for browsing while the second is that the tab bar is removed from the top location adding more space for the actual website.