We conducted demonstration experiments to promote the use of open-source software on desktops as a part of the Open-Source Software-Utilization Development Program for the education sector. In these experiments, we found some barriers to popularizing the use of open-source software in end-user desktop applications. In this paper, we report some typical problems of Web-browser compatibility, which are considered to be obstacles for promoting open-source software on desktops. We also introduce a tool that we developed to help developers avoid such pitfalls while designing Web applications.