Now the photos are visible in the mail header, which is great, but It would be perfect if we can see the contacts photos (avatars) in the Cards view in the mail list.
This is a good idea. If I remember correctly, I think they even did that in a preview screenshot for what was going to be in the cards update, quite a while ago.
It may seem frivolous, but seeing avatars in my mail list is important to me. I am really liking Thunderbird, but get tempted back to EMclient for the avatars