If you are trying to access an old internal corporate tool, school website, or legacy device (like an old router or IP camera), here is the breakdown of why it fails and the workarounds.
If you must use an older version of Firefox to run a specific applet, Firefox 52 ESR (32-bit) is the last version that officially supported the Java plugin. activate java in firefox
A: Some Java applications can be launched via Java Web Start (JNLP) . This allows you to download a small file that launches the application outside of the browser entirely. If your service provider offers a Web Start option, this is the best way to use Java without modifying your browser. If you are trying to access an old