You might notice that scrolling with the mouse wheel or space bar is a bit more jerky than you are used to in Mozilla Firebird. This is because of a feature called Smoothscroll which seems to have problems on OS X. To turn it off, type ‘about: config’ in your URL bar, scroll down to ‘general.smoothScroll’, double-click it and set the value to false.
Smoothscroll not so smooth on OS X
That helps tremendously. I was using the Smoothscroll extension, it was helping but the scrolling was real slow.
Now I have normal scrolling back!!