As for another client: I'm not sure of any better ones. We can try a Java-based client but that has a lot of problems (like being blocked, required Java to be installed, etc.) If anyone has any suggestion please do post them, or email them to technology@tarvalon.net (and cc sysadmin@tarvalon.net...
We don't control any of those adds, in fact the mibbit page is not hosted on our servers at all (we redirect you to their widget).
The best option would be to put a complain into mibbit themselves.