Currently, fonts for icons are apparently loaded from http://s.theoldreader.com even when using https. If one's browser is configured to block mixed active content, this may cause icons not to render (even while letting, e.g., external images in feeds will work fine). For example, setting the security.mixedcontent.blockactivecontent hidden pref in Firefox (to be default in Firefox 23 -- https://bugzilla.mozilla.org/showbug.cgi?id=834836) will break icons.