good morning atolboo,
it worked! did add the boolean as you suggested (see attachment) but, alas, no play... :'(
but you've pointed me in the right direction: after downloading and editing the mediaplayerconnectivity-0.9.3-fx.xpi file, as seen on your link
, it worked.
looks like one doesn't even has to edit about:config (best place of ff and t-bird), nor install vlc player. during the mpc set up one can choose the default installed mm player. maybe quality can be an issue (vlc does a very good job, afaik)?
so i attached the for ff5 modified .xpi too
(ldevelopment stopped at 3.9.x?)
, just remove the .txt at the end and install in ff5.