I think that the issue is between web rep and the browser in Firefox as the extension and uninstall of same are are held in web rep on the browser Add-ons. and in Firefox under Tools > Add-ons it has Avast ! Online security 8.0.1429 listed under Extensions. If you add Avast to the exceptions or whether you do not you get:

The connection was reset

The connection to the server was reset while the page was loading.

The site could be temporarily unavailable or too busy. Try again in a few
moments.
If you are unable to load any pages, check your computer’s network
connection.
If your computer or network is protected by a firewall or proxy, make sure
that Firefox is permitted to access the Web.
Then a button which says ‘try aain later’.

In Safari it has the same thing about the extension and uninstall in Web Rep and in Safari itself it has Avast listed in the Extensions with a tick against enable. When you click on Safari it says along the lines of 'Cannot connect with http://google.co.uk because the server unexpectedly dropped the connection