Was this combination of Firefox + AVG VPN working fine at home, or is this your first time testing this combination?

Is Bell email a branded version of Yahoo! email? (There have been numerous issues with connection errors on AT&T/Yahoo email, so I wonder whether this is a variation of the problem.)

bell is email in canada worked at home with AVG

It should work from the U.S. as well as many other countries. Make sure whatever exit node AVG is assigned to is on the list.

Using Bell email : Accessing Bell email outside of Canada

You also could try Microsoft Edge to see whether it can connect.

Another user reported a problem with this email site: https://support.mozilla.org/questions/1508632 (unsolved)