Flagfox is a simple Firefox extension that displays a flag icon to represent the current website's server location. Hovering your mouse over the flag will reveal the server's IP address, and double-clicking it provides access to a map of the server, ISP details, Whois records and more.
While this all sounds very basic, it's surprising just how useful Flagfox can be. If you've got used to your bank's website being hosted in your own country, for instance, then suddenly seeing that it's relocated to China is a good indication that you're actually on a phishing site. Quick access to Whois records is always useful if, say, you're trying to verify the credentials of a new online store before you place an order. And just being able to see at a glance that a site is hosted on the other side of the world can help to explain why it might be performing poorly, and reassure you that maybe your ISP isn't to blame, after all.
Flagfox is well designed, too, and requires very few system resources. The flag it displays is determined by accessing its own internal IP address database, for example - it doesn't use any form of online lookup. And in the unlikely event of any problems, you can post questions on the Flagfox forum where the extension's author regularly helps out.
Version 5.0.12 brings "IPv4 & IPv6 address location database updates for February 2015"