Hey Japo, thanks for your suggestion.
Avast is gone now. But is seems no matter what I use now (AVG, CA Internet Security, ZoneAlarm, Bullguard, Webroot), the problem is still there.
IE blocks a lot of sites that used to run perfectly, but ff can still get them.
I wonder if, when deleting Kaspersky, it removed something that it shouldn't have.
But I don't know how I could check that.