Finally, a fix for crappy looking icon-fonts in Firefox for Mac OSX is on it's way:
-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).