According to the below link, java is no longer supported in Firefox 52 and above.
Java plug-in does not work in Firefox after installing Java
This article applies to:
- Browser(s) Firefox
- Java version(s): 7.0, 8.0
Firefox limits NPAPI support (technology required for Java applets)
The 64-bit version of Firefox does not support NPAPI plug-ins, including Java.
Firefox 52 and above
Beginning with Firefox 52 (released March 2017), plug-in support is limited to Adobe Flash, and drops support for NPAPI, impacting plugins for Java, Silverlight, and other similar NPAPI based plugins.
If you have problems accessing Java applications using Firefox, Oracle recommends using Internet Explorer (Windows) or Safari (Mac OS X) instead. Developers and System administrators looking for alternative ways to support Firefox users should see this blog regarding Launching Web Start applications.
In addition, by opening the link https://www.java.com/en/download/installed.jsp from Firefox browser to verify java version, you might receive below message: