Hi Skowy,
does turning off the avast firewall solve the problem? Are you able to browse with webshield enabled and firewall turned off?
Edit: We should first find out what component is the problematic one. So the first step is to rule out the firewall. So please try it with firewall disabled. If it works, we might try to tune the firewall, if it does not help, leave it turned off, and we can try to find out other offending part. To me it seems that something on your system (and it seems it has already seen quite a lot) is messing with the redirect feature in avast! that is used both by WebShield and MailShield. Don't understand however, how tuning down the heuristics sensitivy might help though.
Lukas