I think there are a few red-herrings in the replies. From several other forums, there is clearly something odd in the last two updates of Avast Antivirus, going back to about late August 2013, affecting search engines. Avast! seem to be doing nothing about it, even though the fault clearly lies with them. I have not found a single contribution from avast on any of the forums. Neither have I found a single posted solution that works. When I downloaded 2014.9.0.2007 I noticed a few strange goings-on, such as the fact that Google Chrome was secretly downloaded and installed onto my computer, there was no indication of the file size, no option to change the default download destination, and there was no progress window.

The solution in my case was to disable avast in all browsers, and go back to avg. (I know avg has its own set of “inconveniences”, but at least it seems to protect my web-browsing.) I have still left avast! installed, in case they sort out the problem.

Why does avast appear in browsers’ “Add-ons”, but avg does not? Avg still claims to be fully functional.