That is not possible.

Support for the Java plugin and the Java applet in a browser window is dropped in Firefox 52 release, so you can no longer embed Java in a web page. Firefox 52.9.0 ESR will run the Java plugin as the last Firefox version. 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 and can no longer use an applet to open a Java application embedded in a web page.

• https://support.mozilla.org/en-US/kb/npapi-plugins

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