We are having the same problem. We are running Windows 10 (1803) with both Sophos Endpoint Advanced
(escw_108_sa_sfx) and Malwarebytes 3.6.1 installed.
The issue is that both Sophos and Malwarebytes have Web Protection built into their applications.
When Web Protection is enabled in both applications you can no longer use any web browser.
Edge/IE fail to load pages, Firefox fails to start, and Chrome may open an initial page or two but e
ventually stops working.
You need to disable Web Protection in either Sophos or Malwarebtes. This problem only started in June
of this year, 2018. In Sophos, right click on its icon on right side of taskbar. Open window to configure
Sophos options and disable Web Protection. Hope this helps.