There is an interesting blog post about the “line of death” and Chrome. It refers to the area of a browser that a user can “trust”. There are some parts of the browser that a user can trust because they come from a browser. The rest comes from the content and has a different level of trust. This blog post is musing about this with extensions.

That’s why in Firefox popups that are part of the browser overlap into the “trusted” area. The trusted area is above the dotted line: