- In the location bar, type 
about:config - In the filter bar that appears, type 
font - Locate the line "font.FreeType2.enable". If the value here is false, change it to true
 - Edit the 
/default/firefox.js or /default/unix.js and add a line for each directory with TrueType/OpenType fonts like this: 
pref("font.directory.truetype.1", "/usr/local/share/fonts/TrueType");
pref("font.directory.truetype.2", "/usr/share/fonts/TrueType");
 
Now hopefully mozilla will render fonts better. If not, check this page for anything I may have missed out.