Program understanding relates a computer program to the goals and requirements it is designed to accomplish. Understanding techniques that rely only on source code analysis are limited in their ability to derive this relationship. Application-domain analysis is another source of information that can aid program understanding by guiding the source analysis and providing structure to its results. This paper describes the application of a domainbased program understanding process, Synchronized Refinement, to the problem of reverse engineering the Mosaic World Wide Web browser software. It discusses the domain analysis undertaken, the corresponding source code analysis we plan to perform, and the strengths and limitations of available automated tools.