[Trisquel-users] Abrowser won't let me associate Gnome's mplayer with MP4 files

[amenex]

Whatever app is associated with Abrowser, whenever I try to open an MP4 video  
from an HTML file, Abroswer's app insists that the video file is corrupt.

However, when I save the video file to my Documents folder, Mplayer runs it  
just fine. So does *indows 7, for that matter.

But I've not found a way to associate GNOME's Mplayer with MP4 files in the  
Abrowser preferences.

I'm running Trisquel 7 on a ThinkPad T420.

Trisquel 7 is up-to-date with apt-get.