In order to have a version of Firefox that will still use Javascript, download the two files below, then install this version of Firefox (During the installation be sure to pick a different install location than where the current version is installed. If there is another already installed.) Once Firefox has been installed, close it and run the jxpiinstall.exe file to install Java. Once this installation is completed, open this special version of Firefox and test Java.

(for 64bit Windows)
Firefox Setup 52.6.0esr-64.exe

jxpiinstall.exe

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(for 32bit Windows)
Firefox Setup 52.6.0esr-32.exe

jxpiinstall.exe