I too am somewhat lost at to why the having incorrect system time should cause an issue in firefox if you have the latest build for XP, 52.0.1-ESR. Or why anyone would advance their system time to bump into this issue.

But I pushed it forward 10 minutes and it does stall the ‘loading’ of the page. Then there is the inconsistency if it is only happening on one of your systems.

Why I have no idea, but I still can’t see why anyone would be running (or need to be) with the system advanced. Resetting my system time allows the page to load.

Your average avast user probably doesn’t visit my.avast.com then you have running an incorrect system time, the numbers drop even further.