A few days ago I got my girlfriend’s old PC and set a Debian unstable on it. After installation Iceweasel was taking too long to do the DNS lookup of websites that I was typing into it, something I have never encountered before. After searching over the net, most people seemed to suggest that Debian (for some reason) defaults to ipv6 and apparently when its ipv6 requests don’t resolved properly it falls back to ipv4. So disabling ipv6 should fix the slow DNS lookup problem. Here’s how to disable ipv6 on Debian
-> open /etc/modprobe.d/aliases
-> find a line that says : alias net-pf-10 ipv6
-> change it to : alias net-pf-10 off ipv6
and reboot the machine.
If the problem still persists, go to iceweasel/firefox and type about:config in the url bar. search for “network.dns.disableIPv6″ and set it to true.
Hope this helps anyone else with similar problems.

[...] After searching over the net, most people seemed to suggest that Debian (for some reason) defaults to ipv6 and apparently when its ipv6 requests don’t resolved properly it falls back to ipv4 More here [...]
[...] After searching over the net, most people seemed to suggest that Debian (for some reason) defaults to ipv6 and apparently when its ipv6 requests don’t resolved properly it falls back to ipv4 More here [...]
To disable use of on Lenny and Etch: echo “install ipv6 /bin/true” >> /etc/modprobe.d/local.conf (and reboot for the changes to take effect). From Squeeze onwards, IPv6 is built into the kernel, add the kernel command line option “ipv6.disable=1″ to your bootloader
Just installing resolvconf fixed it for me.