Rated 2 out of 5 stars
When I first tried Firebug, I loved it. It was like a dream come true. The dream has soured over time, however, as with every new release of the tool something about it gets worse. First it was support for pages with nested iframes into which sub-pages would be repeatedly loaded. Worked OK pre-1.0, but after 1.0 it just stopped working. Then there were the 1.0 performance issues, whereby after a few hours of use some Firebug activity would start to consume vast amounts of CPU time on every single new page load.
Now I try this new version (admittedly a beta, but beta 3!) and as far as I can tell it doesn't work for me at all. The initial behavior of the disabled parts of the tool is really annoying. Worse, errors that the Firefox error console reports are completely ignored by Firebug. The whole point of my installing it was to get a stack trace - just one little stack trace! - for an exception inside some sloppy Prototype.js code, and Firebug is worse than nothing at all.