Yes there is, it's called FxSpy and it allows you to inspect your application in much the same way as Firebug. Another really nice feature of FxSpy is that you can make changes on the fly and see the effect immediately.

The product is free but you need to incorporate it into your application by making a call to the component which in his turn will open a window.

You can download it from here (project website):

On the wiki there is an installation instruction: