ieSpell

  1. Firefox comes with that automatically...and it's been using it for some time now. Aside from that, you can add on mouse gestures to navigate through web pages (ie slide mouse back, it goes to the previous page), a current and extended forcast bar at the bottom, right click dictionary look up, a multitude of custom skins, session saver that reopens the last page(s) you were viewing upon open...etc etc.

    www.firefox.com