Once the add-on is installed you will see a bug picture on the right-hand side of the browser.
Click on the bug on the browser and you will be able to see Firebug at the bottom of the screen.
Now when you need to find an element click on the arrow highlighted in the following screenshot and place it on the element you need to identify. In this example its the Google search field:
Once you do that, you can see the XPath visible as shown in the following figure:
This technique doesn't work for complex applications where you need to identify your locators by yourself but can be useful most of the time.
And finally to conclude this chapter...