After reading more (see How to Use Java, Silverlight, and Other Plugins in Modern Browsers and -ticking-java-browser-plugin-will-deprecated-soon-1315 46.html), Safari has been one of the longest browsers to support the NPAPI Java plug-in. That support seems to have ended with Safari 11. There are some alternatives according to the jaxenter.com article, but they require modifying the Java application.