Firebug, the well loved Firefox debugger, has something of a struggle on its hands, assuming it has hands, because of the way its host browser is attempting to make it obsolete. Can the new version keep it glowing for a while longer?
Firebug 1.11 will run on Firefox 17 to 20 and it brings some interesting new features. These are mostly small, but they might be enough for you to continue using Firebug over the built-in debug features of Firefox. For example, the Net analysis will now show if the server is using SPDY or not and you can get additional graphical data on the performance of the page load.
If you like working with "live" HTML, then the CSS query selector will be fun to use. You can now pick a selector in the CSS and get all of the elements in the page that match it. You can also now copy and paste entire chunks of HTML into the live page - including SVG and XML. The chunk can be injected at the current node, as first or last child etc.
You can also now monitor and work with the HTML5 cross-windows messaging more easily as the messages are displayed complete with origin, data and target in the console.
There are some other minor improvements including log styling via CSS, logging of function calls and DOM selectors.
The real question is will the slightly flashy new developer tools in Firefox eventually see the demise of Firebug? It would be better if there weren't two teams trying to build the same features or is it that competition is what makes for greatness.
At the moment I still find that Firebug is an essential extra to my use of Firerfox, but this could be because I know it and its commands.