The .woff fonts standard mime type has changed from application/x-font-woff to application/font-woff.
With x-font-woff several browsers throw console warnings
s3cmd picks up the mime types from the system's local copies of the MIME database. It doesn't have any mime type listing of its own to maintain. The fix is to update the system local database.
On Fedora, this is in the shared-mime-info package.