There are a lot of tools available to check IP address but they require to visit some online websites. That consumes some time. But here is a Mozilla Firefox add-on that can easily display your IP address on the status bar of Firefox.
Live IP address is a Firefox add-on that retrieves your live IP address and displays it on status bar of Firefox.
You can easily copy your IP address to clipboard by double-clicking on the IP address field in Firefox’s status bar. It is compatible with Firefox version 3.1b2