Following an upgrade to Firefox 5.0 I found it difficult to scroll pages, particularly if they contained images. It was as if the page was taking a long time to load. A search of the forums suggested that this has been a problem with Firefox since v3 but not something I had previously experienced. However the solution for me was quite simple. Click on the menu toolbar: Tools>Options>Advanced>General>un-tick "use autoscrolling"! Bingo back to smooth scrolling.