Continue shopping in popup does not work in IE 11 & FF

[stawebnice]

Hi,

I have an eshop on VM 3.0.9 at Joomla 3.4.1

There is an issue when you add something into cart and on the popup click Continue shopping, it redirects you to a page with error popup saying> Sorry, article was not found.
This only happens in IE (11), Firefox. In Chrome it returns to previous category without any message.

http://imtp.me/9ogn02lj3 here at http://www.vintagelab15.com it is in Dutch

Please advise how to fix it...