As a workaround solution, you can try to use gecko-mediaplayer which, as far as I can tell, works ok with firefox 3.0 (this is from the same author of mozilla-mplayer and it is using gnome-mplayer as a front-end to mplayer).
As a workaround solution, you can try to use gecko-mediaplayer which, as far as I can tell, works ok with firefox 3.0 (this is from the same author of mozilla-mplayer and it is using gnome-mplayer as a front-end to mplayer).