It is not easy figure out what you are trying to do.
Well, if you have Fedora 14, if you do not have a reason to use the latest mplayer build, then install all of it including the gnome-mplayer firefox plugin from the rpmfusion repo. Then you do not have to worry about all this.
If you do not use rpmfusion, already then you can install it from http://rpmfusion.org
. Then install the package gnome-mplayer. This installs all the other packages including a firefox plugin.
When you run something in the background and it stops, that is because the application is trying to write to the terminal, which it cannot do as it is running in the background. It hangs until you fg
it, and give it access to the terminal. If you want to prevent the hang then route the terminal output to null or use nohup.
gmplayer <file> >/dev/null 2>&1 &
nohup gmplayer <file> &