The latest Firefox version 52 does not support NPAPI plugins including, Java, Microsoft Silverlight and Adobe Acrobat, while the Adobe Flash remains in place.
Over the past few years, Firefox has implemented various Web APIs so that websites can do the same things they've always done without plugins, so you will most likely not notice any change to your browsing experience.
The internet is full of websites that go beyond static pages, such as video, sound and games. NPAPI plugins, especially Flash, have helped enable these interactive pages. But they also make your browsing slower, less secure and more likely to crash.
Over the past few years, Firefox has worked hard to build replacements for these plugins. Together, they are called Web APIs. They are designed to replace the function of these plugins.
Firefox joins other modern browsers like Google Chrome and Microsoft Edge to remove support for these NPAPI plugins.
In case you're not yet ready for this transition to happen, the ESR (Extended Support Release) of Firefox 52 will continue to support these plugins until early 2018.