misc. thoughts :
note : (*if there is another thread dealing with this particular problem i did not look for it first.*)
Sounds like you are waiting on a network response, get tired of waiting and close firefox while firefox is waiting on a network response and ignoring your mouse...
are you having a DNS problem? - try using your own dns server
I have no problems on my linux box or on an 98 box using the linux for dns, but the XP computer using the my ISP dns servers has timeouts a couple times a week.
is this the ipv6 delay
see this post
what else is your box doing at the time? - when yum update is running, my box is really slow....