"Someone could be trying to impersonate the site and you should not continue.

Websites prove their identity via certificates. Firefox does not trust danielvaughn.github.io because its certificate issuer is unknown, the certificate is self-signed, or the server is not sending the correct intermediate certificates.

Error code: SEC_ERROR_UNKNOWN_ISSUER"

To continue to your site, I'd have to click the button "Accept the Risk and Continue", which not everyone will do. I just want you to know in case you want to look into it.