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) 64-bit Firefox
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. Firefox 52 ESR 32-bit release
Mozilla offers an Extended Support Release (ESR) version of Firefox specifically for use by organizations who need extended support for mass deployments. Only Mozilla Firefox 52 ESR 32-bit release will continue offering support for the standards-based plugin support technology required to launch Java Applets. To see if you are using an ESR release, check the Firefox menu item (Help -> About) and looking for the "ESR" identifier.
Mozilla maintains Firefox ESR Releases for approximately one year. Developers and users still relying on the Java plugin technology in the 32-bit Mozilla Firefox web browser should consider migrating to a different solution. Related
firefox joined other modern browsers like edge and chrome with that move. even oracle the creater of the java plugin is advocating for a plugin-free web :-) https://blogs.oracle.com/java-platform-group/moving-to-a-plugin-free-web