Initially the only adapters (host device) shown within virt-manager were macvtap. i.e green0p0 : macvtap
At this time, bridge had been set i.e /var/ipfire/ethernet/settings GREEN_MODE=bridge
The problem was, that under GUI Zone Configuration, the green ethernet adapter was set to ‘None’. After this was changed to ‘Native’, the correct bridge adapter appeared in virt-manager - Bridge green0 : Host device green0p0.