Show the IP address(es) of the current page that you visit in the status bar. It also
allows querying custom services by IP (right mouse button) and hostname
(left mouse button), like whois, netcraft. Additionally you can copy
the IP address to the clipboard. This extension was formerly known as
ipv6ident.

Download the Firefox add-on, click here.

This add-on very useful because you don't have to open a command prompt or application.