At home I have 4 computers running; two have XP as operating system, two Vista. The "Browser stops problem" only occurs on the two Vista laptops, not on the XP laptop and XP desktop. Problems have started since an automatic Vista update about a week ago. What all four computers have in common is the network adapter, all run Avast AV and have Zone Alarm as Firewall. Problems occur with all browsers, Firefox, IE7 and Chrome.
On one of the VISTA laptops (an Asus F3S, CPU Duo T7500, 3GB memory, Vista Premium) I completely uninstalled ZA and reinstalled it, at first the problem seemed to have disappeared, but ... unfortunately, it hasn't. Firefox hanged again, and like one of the previous posts, I had three firefox processes running and could kill only two (and could not restart Firefox). FTP and other internet services remain available, occasionally I can still start and use Chrome, but most of the times I cannot.
Just thought I'd share this with you all, as there is quite some overlap in problems, and I really would like to have a normal internet connection again!