Ultimate Branding JS Error - downloadable font: OS/2: bad linegap

Staff: James Morris
WordPress: 4.7.4
Ultimate Branding:
Browser: Firefox 52.0.2 (Build: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Firefox/52.0)

In WP Admin -> Branding, the following JS error is thrown, only in Firefox. This is consistent on both Windows and Mac.

downloadable font: OS/2: bad linegap: -64 (font-family: "icomoon" style:normal weight:normal stretch:normal src index:1) source: http://ss.wpdevtests.com/wp-content/plugins/ultimate-branding/ultimate-branding-files/css/fonts/icomoon.ttf