Hi Matthias,
I’m not familiar with the Freifunk Dresden firmware. Most communities in Germany use a Gluon based firmware, whereas Gluon in based OpenWRT. I’m not sure, weather they use Gluon nowadays or not. But a bridging between your private network and the Freifunk wifi should never ever accidentally happen.
As Stephan just pointed out, they are not using Gluon. Actually, I was experimenting with Gluon myself for this reason when I encountered that FFDD community was established and quite mature so I wanted to try their firmware out in a bunch of nodes to see how it performs (I’m not particularly the biggest fan of BMX though 
).
Thanks for trying to help though.
Cheers,
err404