The site specified an invalid Strict-Transport-Security header - firebug

Question

I am getting this warning in firebug when adding HSTS header.

The site specified an invalid Strict-Transport-Security header.

here is my htacce

Answer 1

As @jhutar mentioned in comments, similarly in my case as I set up the site on the main domain with trusted SSL certificate the problem disappeared. So, the firebug is showing that error only for self-signed(and/or not-trusted) SSL certificates.