^^^ That print screen is from the Font Awesome site at Github.
Edit - I'm using FF 22 and Vista x32.
The fonts display correctly for me in IE.
I checked this forum - Search found 7 matches: font awesome but the results are really old. The newest is from 2010.
I checked out the info at a thread at support.mozilla.org: Why doesn't firefox display properly icons in sites like github and font awesome?
- * gfx.downloadable_fonts.enabled was (and is) set to true.
* In safe mode the fonts still don't show up correctly.
* The thread talks about language setting issues but my set up was (and is) US English.
===
I don't know how long I've had the problem. Hmm... years? Now that I think about it - I remember those ugly rectangles appearing at Github and some porn sites but I thought it was a noscript thing because I use that add-on to disable font-face.
The problem is the fonts are a lot more common now and those ugly rectangles are starting to appear everywhere.
They are FF 22 and Vista x32.