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 htaccess

<IfModule mod_headers.c>
    Header append X-FRAME-OPTIONS: SAMEORIGIN
    Header append Strict-Transport-Security: 'max-age=31536000; includeSubDomains'
</IfModule>

When I remove quotes from the value I get Internal Server Error. Website is being served through https, redirect from http to https is set from apache's site file. SSL certificate is self-signed, if it matters.

mod headers is enabled. Im on debian 7, apache 2.2.

Thanks

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.