I was experimenting with the fancy new OpenType font capability in Firefox 3.5 and I ran into a problem. I was trying to embed a font on a different domain than the page it
If you want to bypass it you could try adding this to your .htaccess:
Header set Access-Control-Allow-Origin *
To answer your question, it's probably related to the fact that since version 3.5 Firefox supports the cross-origin sharing standard.