The GKB is a generic editor and browser of knowledge bases (KBs) an ontologies-generic in the sense that it is portable across several frame knowledge representation systems (FRSs). This generality is possible because the GKB Editor performs all KB access operations using a generic application programming interface to FRSs called the Generic Frame Protocol (GFP). To adapt the GKB Editor to a new FRS, we need only to create a GFP implementation for the FRS - a task that is usually considerably simpler than implementing a complete KB editor. The GKB Editor also contains several relatively advanced features, including three different viewers of KB relationships, incremental browsing of large graphs, KB analysis tools, extensive customizability, complex selection operations, cut-and-paste operations, and both user- and KB-specific profiles. The GKB Editor is in active use in the development of several ontologies and KBs. This paper discusses the design of the GKB Editor fro a graphical user interface point of view, and describes the difficulties encountered in achieving true portability across multiple FRSs.