1. I installed 'linuxpluginwrapper-20051113_7' and added the next lines to '/etc/libmap.conf'

[/usr/local/lib/npapi/linux-flashplugin/libflashplayer.so]
libpthread.so.0                 libpthread.so.2
libdl.so.2                      pluginwrapper/flash7.so
libz.so.1                       libz.so.3
libm.so.6                       libm.so.4
libc.so.6                       pluginwrapper/flash7.so

2. Installed /usr/ports/www/firefox/

3. Created a symlink:

ln -s /usr/local/lib/npapi/linux-flashplugin/libflashplayer.so /usr/local/lib/firefox/plugins/libflashplayer.so

VOILA ! Flash is back in action under freeBSD & Firefox