When Firefox first appeared, it ran on the Netscape Plugins API infrastructure which has now got so old it makes the Spinning Jenny look cutting edge. From March,
Mozilla will kill off all plugins built on the old NPAPI technology will stop working in Firefox, except for Flash.
This means good-bye to Java, Silverlight, and various audio and video codecs.
Once these plugins once were the backbone of the world wide wibble but now they have been replaced by standalone Web APIs and alternative. The old NPAPI plugins will continue to work in the Firefox ESR (Extended Support Release) 52, but will eventually be killed off in ESR 53.
A series of hacks are available that will allow Firefox users to continue using old NPAPI plugins past Firefox 52, by switching the update channel from Firefox Stable to Firefox ESR.