Firewalls are notoriously hard to configure and maintain. Policies are written in low-level, system-specific languages where rules are inspected and enforced along non-trivial control flow paths. Moreover, firewalls are tightly related to Network Address Translation (NAT) since filters need to be specified taking into account the possible translations of packet addresses, further complicating the task of network administrators. To simplify this job, we propose FIRE WALL SYNTHESIZER (FWS), a tool that decompiles real firewall configurations from different systems into an abstract specification. This representation highlights the meaning of a configuration, i.e., the allowed connections with possible address translations. We show the usage of FWS in analyzing and maintaining a configuration on a simple (yet realistic) scenario and we discuss how the tool scales on real-world policies.