IE and Firefox don't allow cross-domain by default. Only Chrome does.
So you have to specify the url in the style sheets, then allow cross domain in htaccess or in the php header settings. For instance, this is what you'll have to do in htaccess.
<FilesMatch "\.(ttf|otf|eot|woff)$">
<IfModule mod_headers.c>
Header set Access-Control-Allow-Origin: "*"
</IfModule>
</FilesMatch>