Firefox Loads Some Sites Very Slow

It happens on Fedora 12 and Fedora 13 with both Firefox and Seamonkey. It turns out it is not a Firefox problem but a problem related to tcp_window_scaling. See the page http://linux.derkeiler.com/Mailing-Lists/Fedora/2010-02/msg00660.html.

To disable it

echo 0 > /proc/sys/net/ipv4/tcp_window_scaling


Permanently

# echo '"# Disable TCP window scaling" > sysctl.conf'
# echo '"net.ipv4.tcp_window_scaling=0" >> sysctl.conf'


Also see http://www.ecr6.ohio-state.edu/window-scaling.html.