Hi,
your description sounds like this thread, except that it is more detailed - tank you for this. 
Please answer these questions to give us an idea what the problem is:
- What does your IPFire setup look like?
- How is your IPFire connected to the internet (DSL/DHCP/…)?
- Does this problem appear again after a reboot?
- If so, what is the output of iptables -L -n -v on your IPFire machine?
- Are there any errors or warnings being logged during boot or while executing the commands you mentioned above?
- What does your firewall ruleset look like (screenshot)?
Also, please post the output of grep unbound /var/log/messages here, since these log messages are related to the DNS resolver we use in IPFire.
Thanks, and best regards,
Peter MĂĽller