In the past it was possible. Several years ago it was possible to run Flash on Android. Adobe abandoned support of Flash on Android around 2013.

Adobe has not supported Android with their Flash Player Plugin since last update on September 10 2013. Besides many sites have long since dropped support of the ancient Flash 11.1.x branch used by Android devices and BlackBerry Playbook.

Besides Mozilla finally dropped support of the old Flash Plugin as of Firefox 56.0 and later for Android. I am not suggesting to and use a old version just to try and get Flash loading in Firefox on Android.

Many sites are going to or have switched to using HTML5 players for video, audio and games to be more cross platform compared to the more limited Flash Plugin platform use.