What operating system is this on?
What Flash Player version do you have installed?
Flash Player version 184.108.40.206 is the most recent version
Firefox 48 is pretty old and Flash Player is only supported on the latest browser version. If possible, upgrade Firefox to the latest version (60) to see if it fixes the issue. If you're on Windows XP/Vista, then Firefox 52 is the most recent version for those platforms (Important - Firefox is ending support for Windows XP and Vista | Firefox Help ). If you're on OS X 10.6 - 10.8, then Firefox 49 is the latest version supported on those platforms (Firefox support has ended for Mac OS X 10.6, 10.7 and 10.8 | Firefox Help )
If the issue continues to reproduce after updating to the most recent version of Firefox (and Flash Player), please see Report a Flash Player crash or error for assistance.