Is it me or should this be like so -

with firewall switched ON on my OLSR-gateway I am pulling around 1MB/s through my OLSR mesh from a non-OLSR network.
with firewall switched OFF I get around 120kB/s.

What gives? Shouldn't it be the other way 'round, if at all? Well miniscule differences should be there since firewall does its thing etc but it should, if anything, be slower than without firewall, not faster?