For mozilla you'll need to edit the following part of mozilla/defaults/pref/unix.js,
Code:
// TrueType
pref("font.FreeType2.enable", true);
pref("font.freetype2.shared-library", "libfreetype.so.6");
// if libfreetype was built without hinting compiled in
// it is best to leave hinting off
pref("font.FreeType2.autohinted", true);
pref("font.FreeType2.unhinted", false);
// below a certian pixel size anti-aliased fonts produce poor results
pref("font.antialias.min", 0);
pref("font.embedded_bitmaps.max", 1000000);
pref("font.scale.tt_bitmap.dark_text.min", 64);
pref("font.scale.tt_bitmap.dark_text.gain", "0.2");
// sample prefs for TrueType font dirs
pref("font.directory.truetype.1", "/usr/X11R6/lib/X11/fonts/TTF");
Be sure to specify the correct path to your truetype font directory.