The free version of Avast was working fine on my 64-bit Windows 7 system. Guilted by the occasional nag screen, I paid to upgrade to Avast Internet Security, after which Firefox started to become unresponsive (briefly) on every web page except those which are textual in nature and very basic. I've rebooted routers, network switches, etc., hoping they were slowing me down but it appears to me that browsing problems began the day I upgraded.
Tips on what to disable to speed up browsing would be appreciated. The only unusual software on my system is Apache web server, PHP, MySQL. AMD Phenom II 955, 8 gigs memory, fast computer, but browsing speed has gone to hell.