If anyone having a jerky/stuttering/lagging when scrolling a webpage in Firefox, here's a fix. Type in "about:config" in Firefox (address bar) and enter general.smoothScroll under filter. Double click on general.smoothScroll to set it to true. Or else just install add-on smoothwheel. I don't understand why they didn't set it to smooth scrolling to true in the first place. First I thought Firefox 3.5.1 was buggy and lagging when tryng to scroll but found out that my IE8 scrolling was very smooth.