This can happen when Firefox has a problem to access locally installed fonts because of sandbox security issues. https://wiki.mozilla.org/Security/Sandbox Type '''about:preferences#content'''<enter> in the address bar. Across from '''fonts and colors, ''' press the '''Advanced''' button. On the bottom, turn on '''Allow Web Sites To Choose Their Own. ''' [v56+] Type '''about:preferences#general'''<enter> in the address bar. Under '''fonts and colors, ''' press the '''Advanced''' button. Scroll to the bottom, turn on '''Allow Web Sites To Choose Their Own. ''' Fonts Information - Detected via Flash http://browserspy.dk/fonts-flash.php?detail=1