When you think of it, it's also a waste of bandwidth to even transfer FontAwesome when I have a working copy in my system's fonts folder.

My concern is that I can't tell Firefox which fonts from which sites with which checksums it shall trust, so I block all of them and rely on my locally installed fonts.

Hopefully I can use this to repair the broken icons while still blocking foreign font files. At first I thought I had to create a custom mapping from CSS class names to Unicode characters, or even icon sprites in cases where I can't find a nice Unicode character for the meaning.