Makes certain file reading even smoother than Adobe, or viewing in HTML. (You'd think I knew what I was talking about.Dis that make sense?) I've only seen it do "e-Pub" files and without all the clutter around your window it moves from page to page with a slight resistance of the scroller. Otherwise you'd not know it was there at all.
Seemed to me to be of above average utility for an extension.
But then there are so many that make my Firefox a whole new browser.