I had several problems opening java-driven pages with firefox/iceweasel under Debian GNU/Linux Squeeze.
One solution is to disable IPv6-only sockets. Then these sockets are able to send and receive IPv6 and IPv4 traffic.
edit
/etc/sysctl.d/bindv6only.conf
change
net.ipv6.bindv6only = 1
to
net.ipv6.bindv6only = 0
and restart procps
invoke-rc.d procps restart
thanks to: cqfd