I'm having a similar issue with my PC's as well every since version 2291 (Avast Internet Security v17.1.3394.0). even showing
https://www.google.ca it just hangs using firefox (i have seen this with other various sites as well). i've notice this on 2 PC's and 2 Laptops.
All Computers: Windows 7 SP1, fully patched up to including April 2017
Avast: Avast Internet Security (Avast v17.1.3394 - 17.4.3482)
Components Installed: File Sytem | Behavior | Mail | Web | Anti-Spam | Firewall | Sandbox |Rescue Disk | SafeZone Browser
Firefox Version: v53.0 & 53.0.2 (has displayed behavior with both versions)
Today when I updated a computer, I rebooted as needed, open up FF and home page (
www.google.ca) just hangs loading.
Workaround to fix: Temp Disable all shields and refresh page and bam, page loads instantly, turn shield back on and problem goes away for any new tab i open. even after closing firefox and opening it back up. (no reboot of machine).
I only started to see this behavior starting with the February version onward. the january version/s was ok.