I’ve been stalling and delaying upgrading from avast! Free 8.0.1497 for months! Finally accepted to upgrade today when warned my version is out of date - I just let it update and opted for the free 20 days trial of AIS. No problems whatsoever, everything works, no firewall issues at all. Perhaps doing an uninstall and fresh install might have been neater but doesn’t appear to matter. 
I was very worried reading posts over the past months about users saying avast! is now buggy and even going to another vendor.
I noticed I could have got a free 30 day trial of AIS from http://www.avast.com/en-gb/int-30-60-is-trial which is being doubled to 60 days for free. Oh well, never mind?