Hi there,
What browser are they not displaying in? All of them or just Firefox?
If just Firefox, it’s most likely an issue with the url.
Firefox won’t display font icons from a url that doesn’t match the base URL of the page your on.
So if your website is set to http://www.yoursite.com and you visit yoursite.com (no www), the icons won’t show (as an example).
So your first step is to make sure the URLs in Settings > General are both identical.
Let me know ๐