Firefox and Thunderbird not connecting to the internet in Linux

Q I am running a dual-boot system with Windows XP and various Linux distros using interchangeable caddies. My box is connected to the internet by means of a Netgear DG632 router, which has proved OK in most situations. My preferred programs for browsing and mail are Firefox & Thunderbird, and these work fine in XP - but in any of my Linux setups they refuse to connect to the internet. The only way that I can connect satisfactorily is by using Konqueror and KMail. I do not use proxies and I have made sure that all my settings are identical.

A This is caused by Firefox and Thunderbird trying to use IPv6 to connect to the internet, while KDE programs default to the older, more widely supported IPv4 protocol. If your ISP does not use IPv6 and your router does not support it correctly, you'll see exactly the behaviour you describe. There are two possible solutions. The most elegant is to upgrade the firmware of your router. Some Netgear routers certainly benefit from this, correctly handling the fallback to IPv4 after a firmware upgrade. You can get firmware upgrades for Netgear products from support.php. The alternative is to disable Linux's IPv6 support, so Firefox doesn't even try to communicate with the router in this way. You disable IPv6 by adding or editing these two lines in your module configuration file.

alias net-pf-10 off
alias ipv6 off

The name and location of the file varies between distros, and you don't say which you have used, so here are the favourites:

  • /etc/modprobe.conf Mandriva, Slackware and SUSE
  • /etc/modprobe.d/aliases Fedora, Debian & Ubuntu
  • /etc/modules.d/aliases Gentoo

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