EDIT: This post only covers IPv6, please check the update post which covers IPv6 and Firefox
Today when I rebooted to my Windows installation which I very rarely do, I noticed that browsing under Windows feels much faster than under Ubuntu. After booting back to Ubuntu I noticed the “looking up domain.tld” part was taking a lot of time, which seemed a little odd.
Anyways, after some googling I found out that Debian enables IPv6 by default and uses that before and uses it before IPv4. A quick remedy was:
sudo vi /etc/modprobe.d/bad_list #Add this line alias net-pf-10 off
After which you should reboot your system. Now browsing feels much faster. To speed it up a little I installed a local caching DNS server which works like a charm. A quick HOWTO can be found here
Hope this helps.