Firefox doesn’t allow cross-domain fonts and it is breaking the web.  

"Firefox (which supports @font-face from v3.5) does not allow cross-domain fonts by default.  This means the font must be served up from the same domain (and sub-domain) unless you can add an “Access-Control-Allow-Origin” header to the font." - Geoff Evason

Link to the bug: https://bugzilla.mozilla.org/show_bug.cgi?id=604421

Read more:

• http://www.red-team-design.com/firefox-doesnt-allow-cross-domain-fonts-by-default
• https://github.com/MaxCDN/bootstrap-cdn/issues/196
• https://github.com/FortAwesome/Font-Awesome/issues/2044
• http://support.mozilla.org/en-US/questions/956597
• http://stackoverflow.com/questions/17993444/firefox-css-font-face-quirks
• http://geoff.evason.name/2010/05/03/cross-domain-workaround-for-font-face-and-firefox/