May be this is a silly steps. But it works for me.
Testing / Unstable Environment.
su to root first.
// Install free SWF player for flash, and mozilla-firebird browser
apt-get install swf-player mozilla-firebird
// Change to plugins directory
cd /usr/lib/mozilla-firebird/plugins/
// Create backup folder
mkdir ../backup
// Move uncertain plugin ...
mv ./libnullplugin.so ../backup
// Link Mozilla plugin to Mozilla-Firebird
ln -s ../../mozilla/plugins/libmozswfdec.so .
// Done.
Is there any other better method up to now ???
Any idea what the libnullplugin.so is, except it is a null plugin ???
Have fun.