Just discovered this - Chris Blackwell has released a Firebug extension that adds Model-Glue debugging to Firebug. I'm primarily a Chrome user now but this would tempt me back to Firefox just to get this. (And don't forget ColdFire as a Firebug extension as well.) Here is a sample screen shot from the extension running on my local Model-Glue application.
Just in case that isn't obvious - that's Model-Glue debugging data not within the main page layout but rather in the chrome of Firebug itself. It can provide you with all the information you need without cluttering up your fancy web page design. Awesome.
One quick note - I was not able to get this working with the latest Firebug beta that works with the latest Firefox beta. Stick to the released builds of both and you should be OK.