One of the main objectives of FWSM 4.0 is to provide close integration and collaboration between FWSM and other Cisco Catalyst 6500 Series Switch services. This paper provides technical details for integration of FWSM4.0 with the Virtual Switching System (VSS).
The integration and deployment of FWSM in a VSS environment are done transparently and do not require special configuration. There are only minor changes on the Cisco Catalyst 6500 Series side that need to be considered, and these are very much contained within the changes that are inherent to VSS model of Cisco IOS Software.
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps9336/white_paper_c11_513360.html