Install the Java-Plugin for Firefox

To install the Java plugin for Firefox, you have to create a symlink from Firefox's plugin directory /usr/lib/firefox-addons/plugins/ to the file libnpjp2.so in the JRE's “lib” dir.

sudo ln -s \
  ${JAVA_HOME}/jre/lib/amd64/libnpjp2.so \
  /usr/lib/firefox-addons/plugins/libnpjp2.so

Please note, that I tested this with Ubuntu 14.04, the “plugin” directory may be somewhere else on your system.