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.
Download or Waterfox Classic . Do not use this for general browsing (banking, email, social media). Disconnect from the internet if possible. activate java in firefox
This content is primarily for historical/legacy system reference . Modern Firefox versions (Version 52+, released March 2017) do not support the Java plugin due to security risks and the deprecation of the NPAPI architecture. If you must use an older version of
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. Disconnect from the internet if possible
Disclaimer: These steps do not work on modern Firefox versions (v53+). They are provided for understanding legacy systems.