Sorry, I just realized I commented this in a thread that was marked resolved. So I'm posting it on it's own thread.
This is something I've encountered on the Samsung Galaxy Tablet. All my icons show up expect for the 'f' for Facebook. I use it in two places on the website, and have used CSS to target the top bar to be different. I tried disabling this, and just using it in one place, and clearing the CSS I added, and still no 'f' for Facebook showing. All others work great
This is a website I have started working on for my friend: