No sound HDMI in Firefox due rosa mplayer plugin

[lucodp]

Hi,
I am new user with ROSA.2012.MARATHON.X1.

I configured my TV with HDMI output and duplicate screen in video card configuration (my video card is Nvidia)

Sound test with HDMI works, notifications also, but youtube video in firefox doesn't work with HDMI because Firefox use rosa mplayer plugin as a default.
The solution will be use VLC web plugin, but is this plugin in the repositories??? Where????

Thank very much for your support

Lucodp