I've just started using Avast this week, and have experienced a problem with Firefox/internet. Avast automatic updates was on, and I noticed that if I went onto internet and an update was available, it downloaded OK (and a message came up to say that it had done so) but then Firefox would freeze. If I exited Firefox I could not get access to internet again, and had to reboot computer in order to do so. I've now turned off automatic updates, in order to see if this cures it OK.