Firefox is very 'jumpy' since i updated to xp service pack 2?

ok i'm running windows xp service pack 2 which i have just updated from service pack 1 when i updated firefox starting becoming 'jumpy' when im scrolling up and down webpages

when scrolling up and down you can see lines moving down the page 'updating' the display to the new bit of the web page

i have tryed installing that smooth scrolling addon and all it done were to create more lines at current it looks tacky and bad ive tryed re-installing firefox but nothing

(i have also installed avast anti virus)

if its the anti virus will some1 tell me how to test the anti virus too see if thats the problem without putting my computer at risk

Firefox is very 'jumpy' since i updated to xp service pack 2?virus removal

it might be your monitor frequency fps thingy. on desktop, right click and then click properties, click the setting tab, click advance, then click the monitor tab and change the monitor thingy from like 60hz to around 80-100hz, apply and save. and hopefully you see a difference.