The Firebug team have released Firebug 1.5, with many bug fixes and new great features below:-

• Mike Radcliffe’s Inspector. Firebug's key feature, now solid as a rock,
• Jan ‘Honza’ Odvarko’s expanded and refined the Net panel, with more accurate timings,
• Steve Roussey’s reworking of HTML editing and entity support,
• Kevin Decker’s CSS and Style side panel improvements,
• Support for dynamic, graphical breakpoints throughout Firebug.
• It works with the soon-to-be-released Firefox 3.6

Most importantly, it is released before Firefox 3.6. The biggest problem is upgrading Firefox and finding Firebug no longer works.