The mozilla webplugin supports only the libvlc_MediaPlayer* events just like the ActiveX webplugin.
Ommit the 'libvlc_' prefix from the libvlc_MediaPlayer* events to obtain the events name that must be
used from JavaScript to listen on the event. Example:

- libvlc_MediaPlayerOpening becomes 'MediaPlayerOpening'
- libvlc_MediaPlayerNothingSpecial becoms 'MediaPlayerNothingSpecial'