What are your standard shield settings?
You may be able to set it so it is not to sensitive but still provide adequate protection.
I still find it a little odd that standard shield that only scans hdd content could slow internet connection speed. Unless the high priority setting of ashServ.exe (the actual scanner for standard shield, etc., see task manager Processes) takes up cpu resources there by slowing the web shield scan (ashWebSv.exe) which could show up as slowing download speed. This is just my theory, not fact but it might explain the difference with IE and firefox when standard shield doesn't scan the extension less files in firefox's browser cache.
As a dial-up user I would give someone's right are to see my connection speed drop to 4500 mbps
