try disabling it in Iceweasel/Firefox first if it works disable it system wide.
In a nutshell:
about
:config
in the filter field, type “DNS” and hit enter
double-click on “network.dns.disableIPv6″, changing its value from False to True
In a nutshell:
about
:config
in the filter field, type “DNS” and hit enter
double-click on “network.dns.disableIPv6″, changing its value from False to True
You may also try something like: Speedup DNS requests with a local cache -
http://www.debian-administration.org/articles/390
But just disabling ipv6 should fix the issue.