Add this missing mime type  to Mimetypes.js & should help.
less -> text/css
woff -> application/x-font-woff
eot -> application/vnd.ms-fontobjec
Whereabouts does Mimetypes.js live ? Is it within the JCR repo ?
5.6 should already have it . Please add at http://<host>:<port>/crx/de/js/CRX/util/Mimetypes.js & verify.