HOWTO Disable IPv6 support on Debian
This article is incomplete and was first written in July 2006 for the BeezNest technical website (http://glasnost.beeznest.org/articles/342).
IPv6 is still not widely accepted and even less used. Many networked applications in Debian are enabling IPv6 support anyway, which result in a drop in performance and longer delays in day-to-day use.
The effort to do the opposite (ie activating IPv6 throughout Debian) is located here: Debian IPv6 Project
To disallow ipv6 kernel module autoloading, deactivate it in modutils  or module-init-tools in /etc/modprobe.d/aliases.
To disable IPv6 name resolution in Firefox or other Gecko-based browsers, change the following option to true:
 deprecated for kernels 2.6+