One of the most annoying “features” of Firefox 3.0 was the new “user-friendly” warning that shows up when you try to connect to a site using https, and it’s certificate is self-signed or has expired. In most cases, the warning can be safely ignored, but Firefox forces you to go through three extra mouseclicks to continue to the site. 

A plugin by CMU allows you to skip this in some case. The plugin will query a number of Perspectives-servers, that will check whether the site looks the same from different locations, thus defeating man-in-the-middle attacks. If the site is trustworthy and all servers see the same content, the plugin gives you the option to suppress the security warning and lets you continue without unnecessary interruptions. 

A small icon notifies you that Perspectives has verified the site you are visiting, and doubleclicking it lets you view information about the site and it’s certificate(s).