Font Icon not showing in FireFox 30.0

[SGM-IT-AC]

I've tried using IE 11 and the font icons on the menu option display, but they are not showing in FireFox. I tried a local copy on my Windows 7 machine and on a Windows 7 machine running WAMPserver 2.5 with the same result on both.

In FireBug 2.0.1 the first icon that doesn't display has:
.fa-envelope:before { content: ""; } in font-awesome.min.css. Between the quotes is an image of a square.

Is there something that has to be enabled in the FireFox browser to display the icons?
There are no errors or warning on the screen.

[onokumus]

@DuckieDude
Please try following code

<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/font-awesome/4.1.0/css/font-awesome.min.css">

and tell me result.

[SGM-IT-AC]

Yup, that worked. Thanks :)