How To Disable IPv6 In Ubuntu 9.10 Karmic Koala

If your browsers work OK, you do not need to disable IPv6. Also, there is nothing wrong with either Ubuntu (Karmic) or IPv6, so if you are experiencing any issues, they are because of your ISP / router / modem.

Symptoms there is something wrong with your ISP / router because of IPv6 can be: Firefox works badly or Firefox works OK but Opera does not (and there is no way to disable IPv6 in Opera) or if you leave Firefox open for some time and Google works but you cannot open any other pages or to make Firefox work you have to restart your PC, etc.