Beginning in Firefox version 52, support for NPAPI plugins in Firefox has ended, except for Adobe Flash. Some of the plugins that will no longer load include Java, Microsoft Silverlight and Adobe Acrobat. See this compatibility document for details. 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.
Why did Firefox do this?
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 without undermining your internet security, stability and performance.
Before, these Web APIs weren’t quite ready, so Firefox started the transition by making plugins load manually (click to activate).
Today, they’re ready. Many sites have adopted them, and almost all your favorite pages can be enjoyed without using old and insecure 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.