When the booking got to an end I had on my screen a page with a QR code and some details. I used the File->Print menu
Today at work I tried to re-enter the site and fortunately using my health card and fiscal code I was able to show the page of the confirmed booking with the QR code, and get it via a screen dump (xv), so nothing was lost, but I am curious to see why such site did produce a blank pdf.
While you cannot get the QR code page (unless you are a resident in Lombardy and perform an actual booking ) the same behaviour occurs already for the home page indicated on the first line of this post. I verified that even if one prints to an actual printer, or does a File->Print Preview, one gets a blank page.
So obviously the site is designed in a Palemoon unfriendly way.
(It did not happen before to me on any other site ... my fault I did not do a preview, though I am usually suspicious and do a page print before pressing any provided pritn button - which some sites do not have and some show on a subsequent page. Next time I'll remember, and/or do a screendump.)