PageZipper is a one of the cool firefox addon which really makes it very simple to go to the next page, it scans the entire page for the text Next and automatically loads the next page when you scroll down at the current page.
After Installing PageZipper you will need to manually activate PageZipper, In order to activate it go to File Menu >> View >> Toolbars >> Customize menu and drag the PageZipper icon on the FireFox toolbar to place it on the toolbar to make is more accessible.