Adobe stopped supporting Android with the old Flash Player 11.1.x branch being the last with last update way back on September 10 20'''13'''. Firefox for Android has dropped support of this old vulnerable Flash Plugin from Firefox 56.0 and later. Even if you could get this ancient Flash 11.1.x version working, many sites have long dropped support of the old 11.1 branch used by Android and BlackBerry Playbook. Also more and more sites are using HTML5 players for video and audio now to be more cross platform. https://support.mozilla.org/en-US/kb/how-do-i-watch-flash-videos-firefox-android