Finally, a fix for crappy looking icon-fonts in Firefox for Mac OSX is on it’s way:
https://bugzilla.mozilla.org/show_bug.cgi?id=857142#c83
-webkit-font-smoothing: antialiased;
-moz-osx-font-smoothing: grayscale;
You have to add -moz-osx-font-smoothing to your css. It works analog to -webkit-font-smoothing and will go live with Firefox 25.
You can already test your icon-fonts with Firefox Nightly 25.0a1 (see link above).