Many possible causes but that should get done--
Copy the "libflashplayer.so" to the folder /usr/lib/flash-plugin/. If plugin/ does not exist you may create it and place it there. Change the permission to be executable to all users
~# chmod 775 /usr/lib/flash-plugin/libflashplayer.so
Or you may copy that file <to be sure> into your home folder: /home/ME/.mozilla/extensions/ place here the "libflashplayer.so" file. The own it, execute it:
~$ chown me:mygroup ~/.mozilla/extensions/libflashplayer.so
~$ chmod 755 ~/.mozilla/extensions/libflashplayer.so
That should work.
Hope this helps. Good luck.