I've been pissed off because firefox and mozilla both run like shit on my fc box. Here is why:
DNS lookups under Fedora Core 2
If you use Mozilla under Fedora Core 2, then this'll interest you.
Users of Mozilla on Fedora Core 2 may experience unusually long delays in resolving hostnames. This results from the fact that IPv6 is enabled by default in Fedora Core 2. If you do not need IPv6 support (which is most likely the case), then it is advised that you disable it in the kernel. To do this run the following command as root:
echo "alias net-pf-10 off" >> /etc/modprobe.conf
You will need to reboot to have this take effect (or simply unload the ipv6 kernel module).
See bug 239358 for details.
NOTE: Disabling IPv6 via the Mozilla preference "network.dns.disableIPv6" is not sufficient. The problem is caused by a change in the behavior of getaddrinfo under Fedora Core 2. When asked to provide the canonical hostname, getaddrinfo performs a reverse lookup on all returned IP addresses. The result is 10 DNS queries for www.yahoo.com
instead of just 1. When IPv6 is disabled in the operating system, Mozilla falls back to using good old gethostbyname, and the problem goes away.
WinXP and older versions of GLIBC (such as those used by FC1 and RH9) do not exhibit this behavior.