I have integrated both FontAwesome icons and some icons from Icomoon into my project. Initially, the FontAwesome icons worked perfectly fine - they were awesome. However, after two weeks, when I attempted to add Icomoon font icons, it caused interference with the FontAwesome icons. This resulted in some FontAwesome icons appearing as boxes ([]) along with all the Icomoon icons.
For a live demonstration, you can check out this example. The [] next to "Comedy" represents an Icomoon icon, while the rest of the []'s indicate broken FontAwesome icons.
Here is the jsFiddlelink