Plugger seems to work pretty badly for me, every time a plugin gets 
run, a zombie is left around that stays there until mozilla is restarted.
Fortunately there's a fix, which is mozplugger (http://mozplugger.mozdev.org/)
that seems to be actively maintained.

The things that have been fixed in it:

- Fixed bug/new feature : The "stream" option of the file pluggerrc has been
changed to make the browser just pass an URL to the player without downloading
the file. The old behaviour is no more supported by Mozilla.
- Fixed bug with Mozilla 1.x : a zombie process was created for each loaded
plugin, until Mozilla exits