From FrugalWiki
Gnome-mplayer
This a GUI of mplayer for the desktop environment Gnome.
Installation
# pacman-g2 -S gnome-mplayer
The plugin gecko-mediaplayer
This plugin wil lpermit you to use gnome-mplayer to show videos in your browser Firefox, Opera…
To install it:
# pacman-g2 -S gecko-mediaplayer