This may be your problem,

All Firefox v52+ Releases disables all plugins except for Flash Why do Java, Silverlight, Adobe Acrobat and other plugins no longer work? {web link}

http://kb.mozillazine.org/JavaScript_is_not_Java

I've found a solution; at least a partial solution. I downloaded & installed the offline version of Java. It works with my Open Office database program that requires a JRE to work. I don't know if I'll also have to install an online version to work with the internet websites (or do the websites that require a JRE to display images already have the JRE available?)

That was very good work. Well Done. Please flag your last post as Solved Problem as this can help others with similar problems.

There is only one JRE version although Oracle offers an offline installer, but that merely means that you download a complete file that doesn't require internet access. You can compare this with the small Firefox stub installer that download files from internet and the full installer that includes all files and that doesn't requires internet access.

Websites need to use Java Web Start (i.e. send a special XML file as application/x-java-jnlp-file) to launch a Java application in an external standalone window instead and can no longer use an applet to open a Java application embedded in a web page. Websites that want to use Java need to adapt and make the change to launch a Java application this way.

A Java Web Start JNLP file is basically a XML file that the server sends as application/x-java-jnlp-file and that is opened by the default application for this MIME type (Java Web Start). Java then handles everything on its own, but there is no longer embedding possible like a plugin offers. Java registers this MIME type when you install the Java program.