Just installed a fresh copy of Ubuntu 13.04 64 and ran into a very strange problem. Chrome is working fine but Firefox sometimes connects to sites very slow. It can take around 10 seconds before Firefox starts to load something(I can see something connecting to or look up).
I actually found out how to fix it. Just go to about:config and set network.dns.disableIPv6 to true and Firefox starts loading pages very fast
But my question is what's changed since Ubuntu 12.10. In my Ubuntu 12.10 network.dns.disableIPv6 is set to false and Firefox works properly.