Safari - proxy settings

Welcome guys!

I am a new macbook air user. Everything is new for me because i used windows since 95 and my web browser was always google chrome.

I have a problem with safari. I would like to use it, but unfortunately i can't.

My university gives access to several sites via proxy.pac (http://sum.edu.pl/proxy.pac). It works perfectly on Google Chrome, firstly i had to login using my university account, password and login were saved by chrome, and now i can login to every site i want.
Unfortunately it doesn't work so well on safari. For example, I don't know why I don't have to login to university account and some sites work very well (like www.ncbi.nlm.nih.gov/pubmed), but site i need the most doesn't work - libra.ibuk.pl (this is polish online library, i can use online books to which my university bought an access).

Of course i've done everything properly in internet settings in my mac because chrome works perfectly (writing the http://sum.edu.pl/proxy.pac in proxy autoconfiguration).

Thank you very much for you help and apologies for my english (if there were any mistakes).