As a related feature request, I like to suggest, that the .desktop file for MuPDF should also register all other supported file types.
MuPDF started as a simple PDF viewer, but it now also supports the formats XPS, OpenXPS and ePub. In my experience, it is a fast and reliable viewer for ePub files from the Project Gutenberg. For a better desktop integration, the .desktop file should register these file types as well. For ePub files it would be: MimeType=application/pdf;application/epub+zip; I don't know about XPS files, though. -- Regards, Hartmut Buhrmester