Flagfox is what Firefox extensions are all about: ultracompact, free, open-source, and uniquely useful. When you visit a Web page in Firefox, Flagfox identifies the country hosting the site's server with a small national flag in the address bar. You can customize the information Flagfox retrieves and displays, too.
We've used Flagfox for several years and always found it useful (and occasionally comforting) to be able to see at a glance where the site we're visiting is hosted, not to mention the bonus of learning to identify some national flags. Flagfox does a lot more than that, though, and we recommend it to all Firefox users.