Compared to Firebug 1.3.0, the 1.3.1 version is more stable, faster and has more cool features. All known defects were fixed (with the exception of one which was partially fixed), considerable performances improvements were made, and the two most popular Firebug Lite features (CSS editing and XHR inspection) received a lot of improvements.
Link.
Firebug on IE6, anyone?
