Hi Rafal
Just to confirm that this is a template related issue, could you try enabling one of the default Joomla templates (Protostar) and see if the issue still exists.
Also we are getting the following warning when we attempt to access the URL provided...
Firefox detected a potential security threat and did not continue to http://www.testsamorzad.us.edu.pl. If you visit this site, attackers could try to steal information like your passwords, emails, or credit card details.
Similar warning in Chrome.
Ciaran