Some FontAwesome -icons not showing on Firefox

Hi!

Some FontAwesome icons are not showing when using Firefox (tested on versions 23.0.1, 32.0.2 and 32.0.3). With Chrome they appear correctly (I haven't tested other browsers yet).

Example here: http://fontawesome.wikidot.com/

Any idea what might be causing this?

Edit: moved the post to Bootstrap Playground, which might be a bit more appropriate forum for this question.