Flagfox can be configured to show the flag and additional information in the address bar or the status bar (left or right), open information in a new tab or window, and define a custom action for middle-clicking on the country flag icon.
Middle-clicking on the flag icon will perform a whois, copy the IP address or open an additional tab with Wikipedia information about the selected country, depending on how you set this action in the Flagfox preferences window.
Custom actions are also supported, the default action (if enabled) will look for pages indexed by Google of the current website. For example, using the default action for this address will return these search results.
Install Flagfox from the Firefox add-ons page