Not really as the only [https://support.mozilla.org/en-US/kb/npapi-plugins NPAPI Plugin] allowed to run in Firefox since the 52.O Release has been Flash Player from Adobe. Many sites have been changing to HTML5 players for video, audio and games now days. This may increase as Adobe stops [https://developer.mozilla.org/en-US/docs/Plugins/Roadmap supporting Flash completely in late 2020]. Mozilla did have Shumway which was a media player for playing SWF files. It was intended as an open-source replacement for Adobe Flash Player however it has been discontinued. http://mozilla.github.io/shumway/