In this paper, we describe our trace monitoring system and a 
methodology for reverse engineering interface protocols to 
capture the sequence of method invocations for large C++ 
applications. To evaluate our system, we present a case study 
using the networking library in the Mozilla Internet Application 
Suite, and three Mozilla applications: Firefox, Thunderbird and 
Sunbird.  We use trace monitoring of the library to capture the 
interface protocols for the classes in the library and our 
preliminary results support our assumption that interface protocols 
follow a specific pattern and that these patterns can facilitate 
comprehension of the underlying interactions among the classes 
in the system.