# nano /etc/sysctl.d/bindv6only.conf
net.ipv6.bindv6only = 1
net.ipv6.bindv6only = 0
# invoke-rc.d procps restart
I have no idea what other positive or negative ramifications this will have to your system, so proceed with caution. I'm pretty sure you can undo any damage by setting the 0 back to 1 and doing the invoke-rc.d call over.
FWIW, the icedtea6-plugin doesn't work either, but I haven't been able to figure out that one.