Smooth scrolling has been implemented in Mozilla. To see it in action, just download a recent nightly build and add this line to your prefs.js file (while Mozilla isn’t running).
user_pref("general.smoothScroll", true);
If you’re not familiar with the feature, smooth scrolling slides text up pixel-by-pixel during a scroll, instead of a chunk at a time (IE also has this feature). This didn’t initially sound very useful to me, either, but this thead on the gtk-devel-list (for GTK development with Linux) conveys that smooth scrolling allows for scrolling & reading the text at the same time.
Sure enough, smooth scrolling does make it easier to scroll and read text in quick succession. The physics of the current implementation isn’t perfect yet (gravity, velocity, and so on), but I still consider it an improvement over regular scrolling.
Nah, don’t bother with the user.js stuff anymore… use about:config! Much easier and you don’t have to shut down the browser.