14 DAY TRIAL // Mozilla is working on a rather interesting set of developer tools for Firefox. It's expanding with each new Firefox as more components are added. A JavaScript debugger is now on its way, promising to be a big improvement over the existing tools.
The new debugger is far from ready, but the code is now part of the nightly Firefox builds, which will become Firefox 13 though there's no guarantee that the debugger will be ready by then.
The JavaScript debugger is planned for release sometime in the third quarter of the year.
The core functionality is there, but the UI is incomplete. In its current state, it's of little use for actual debugging, but there are a couple of things to play with if you're interested in the new tool.
The debugger is not even enabled by default even in the Nightlies, but you can go to the about:config page, search for devtools.debugger.enabled and set it to true. For breakpoints, you need to enable devtools.gcli.enable.
"Firebug depends on the traditional JSD API in SpiderMonkey to perform its magic, but nowadays JSD is limiting in a number of ways. In order to overcome these limitations, the new JSDBG2 API was designed and implemented by Jim Blandy and Jason Orendorff," Mozilla's Panagiotis Astithas, who has worked on the new debugger, explained.
"What's in there right now is not useful for day-to-day work, even for experienced developers. There is no UI to add breakpoints besides the experimental Graphical Command Line Interface (whose awesomeness deserves a separate post), no stepping, no variable inspection besides call parameters and 'this', and numerous other limitations," he added.
Mozilla is determined to build a top-notch set of developer tools into Firefox and that's probably a good idea. Dev tools haven't been a major focus for Mozilla, especially with Firebug around, but the tools in WebKit, found in Chrome and Safari, probably convinced Mozilla that it needs to do as much for developers as it does for regular users.