firewalls have no noticable affect on your downloading/surfing as they do not control the speed process all a firewall does is allow traffic to pass through a preset list of ports allowed and block traffic to closed ports.
if your firewall slows you down then it is your settings that are wrong and not the firewall slowing traffic
as to the initial question as suggested above avg is all you need ditch norton and get it here its free
www.grisoft.com