Have you considered another browser? Just give opera a try. It's smal fast and simple.

When i use ff just the starting up is slow, 15 till 20 sec. And i'am running an amd dualcore 3600 with 1 gig memory.

And on my son's puter an amd Athlon 1200 it takes about the same time.

To much memory is also a slow down unless you are running a 64 bit system. Otherwise thing about overclocking but be carefull. To much power can ruin your system.

One thing to help Firefox run faster is to delete (or at least cut back) on how long you keep the history files. The further back your history files go the longer it takes. Also, if you have numerous add-ons they can affect the speed of Firefox as well.

If you want to scan a file use http://www.virustotal.com/ it scans use a multiple number of virus and security scans.

If you check back through the archives you can find more tips as well.