Thunderbird not retrieving mail

Avast for Mac mail shield broken?
I have Thunderbird, IMAP account and when returning to work on Tuesday, I couldn’t retrieve any mail. Friday, everything was fine.
So I thought at first there might be a problem with our mail server and I contacted the provider. Nothing wrong there.
After some hard thinking I realised Avast mail shield is a possible cause for my problem (Avast works so smooth in the background you never think about it) and so I shut down mail shield. Voilá, all mail came through.

Avast for Mac 8.0 (40005) - defs version 14010701
Mac OS 10.8.5
Thunderbird 24.2.0