Now you don't have to guess what events were bound to which elements!
Also, this article has a good overview of multiple Firebug extensions:
I know some people who love PixelPerfect for transferring Photoshop mockups to CSS.
Also one of the comments mentioned widerbug which I might try now that I have this weird 18.4" laptop:
Great when working with sessions or cookies.
I also wrote a rudimentary Firebug plugin but yours looks way more slick :)
Measure it - adds a ruler to FF for pixel pushing:
Web Developer Toolbar - adds a whole bunch of inspector type stuff
Color Picker - Lets you get the color of a pixel by clicking on it
IE also has similar tools:
Firefox plugin API really needs an overhaul. It shouldn't be assumed that everything breaks on every point release. Firefox needs to come up with an API going forward and stay backwards compatible till the next full version number.
I think Chrome is going to lead the way here. Their plugin strategy seems to be based off fixing the mis-steps of firefox.
Also, they've changed addons.mozilla.org where most addon authors just have to flip a dropdown box to move support to a new version-- no new upload required. Many authors don't know that, so they wait until the full release to change their support.
FF 3.1 should break very few extensions. Almost none of mine died, though Firebug is particularly sensitive. But I used Firebug 1.3.0 betas just fine for a while on FF 3.1. (My new laptop isn't using FF3.1 at this moment, though.)
EDIT: I'd also like to add that this version of Firebug actually does work in FF3.1. It's only that in their install.rdf file, they specified 3.0.*. I changed it to 3.1b2pre and re-built the extension and it seems to work great under Minefield. I think they put the version restriction to prevent people from reporting bugs for the still beta FF3.1.