http://www.a.phys.nagoya-u.ac.jp/~taka/linux/co4note-eng.html#ipv6
Improve the speed of connection to Web sites
The reason why the resolution of the name of web sites take long time is that the Mozilla is forced to try IPv6 first. Since the IPv6 is rarely used, turn off it. At the end of /etc/modprobe.conf, add
# Turn off IPv6
alias net-pf-10 off
alias ipv6 off
and reboot.