The avast! Home Web Shield doesn’t like Flock. I - and other Flock users also - am having problems with it. Flock is a Firefox-based social web browser which can be found at flock.com.
Take a look at this:
http://extensions.flock.com/faq/show/28#q_4580
http://bugzilla.flock.com/show_bug.cgi?id=4236
Is there anything I can do about this, except disabling the Web Shield?