playing videos in mozilla

My home desktop is running RH9 with the installed mozilla that came with it. I installed mplayer this evening, so now it is able to play movies. The problem being that it won't just play a movie file once, it keeps playing it over and over.

in edit-preferences-privacy-images I've got animated images should loop set to once.

I've had other incarnations play the mpegs etc. in separate windows, and they've only played them once. I can't figure out how to get this to happen.