umm, is this the linux version of firefox or native?
if its native then i am not sure if its possible to use a linux library (/usr/home/disappearedng/.mozilla/plugins/libflashplayer.so) without some shim/hack.
i don't use firefox or flash on fbsd so others may be able to offer more pertinent advice.
have you checkedout this thread:
http://www.daemonforums.org/showthread.php?t=2225?