NoScript on Firefox solves that problem. Yes it breaks a lot of pages, but then you get to fiddle about allowing and banning different scripts to see what's doing what. Probably not for everyone but I like the educational value.

[Edit] So that pop-up is coming from mailchimp_com, which is called by list-manage_com, which in turn is called by s3amazonaws_com. So blocking that last one is all you need.

In fact this is quite a great web site, as it displays all its content even if you completely disable all scripts.