Testing Graphical User Interfaces (GUIs) is difficult, involving many states, inputs and events. Another serious problem is that in testing GUIs, not all effects created by the testing are observable. We have previously reported a scalable method for testing GUIs based on Complete Interactions Sequences (CIS). A CIS is a sequence of GUI objects and selections that collaborate to produce a response for the user called the responsibility. In this paper we use the CIS foundation to develop a new firewall method for GUI regression testing. This new method is an inherently selective regression approach in which only GUI objects in the firewall need be regression tested. An empirical study of a commercial GUI system is used to illustrate this new method.