I am using Window 7. I have very serious problem with speed in firefox when connected with internet. It works very slow. When I tested without internet it was working normal. I have tried various anti-virus tools and adware removal softwares. I also contacted with internet service provider. But when I test internet speed it shows around 2 MB or enough desired speed.

I also replaced my hard drive in the doubt of any damage. I am using dell-3500 laptop with intel i3 core processor (32 bit OS) Surprisingly when I uninstall and re-install firefox browser it shows always previously installed adons and setting looking like using old settings. Sometime but not always it also shows the popup like : "some type of script is running . do you want to debug or stop". Now going to be very frustrated not able to detect exact issue of slowing down of browser. Sometime so slow that if I scroll down with mouse it jerk and take few seconds to shift only one inch downward and when I open new tab it takes 20-30 sec to open new web page. I am looking for any help.