Started up Firefox just now and the automatic updater told me that Firebug 1.0 is now available. Of course, I immediately upgraded. The visual look has definitely seen some work and there are a number of new features - see the screenshot to see a loading time breakdown of all the elements of this page.

This, coupled with the 1.1 release of the Web Developer Toolbar (my favourite new feature - it is now possible to validate local pages) and the release of Prototype 1.5 (now with documentation!) last week, makes it an exciting couple of weeks for web developers everywhere.