Saw the subject article at BC, Mozilla to Drop Support for All NPAPI Plugins in Firefox 52, Except Flash, and went looking for more information at Mozilla and found this: Plug-in support has been dropped other than Flash (Affecting) | Firefox Site Compatibility.
Bottom line, if you absolutely must use the Java or other NPAPI plugins and wish to continue using Firefox, you will need to switch to the ESR version which will allow those plugins to be enabled until May 2018.
Bottom line, if you absolutely must use the Java or other NPAPI plugins and wish to continue using Firefox, you will need to switch to the ESR version which will allow those plugins to be enabled until May 2018.