For years, an extension called Firebug has been a powerful tool that kept Web programmers loyal to Firefox.

But now, as browser makers add their own tools geared to attract those who build Web sites and applications, the lead Firebug programmer has taken a job with Chrome, CNET has learned.

"Monday, I start work on next-gen Web dev tools at Google on the Chrome browser team. Consequently I will no longer be contributing routinely to the development and maintenance of Firebug for Firefox," John J. Barton told members of a Firebug mailing list yesterday.

The change reflects the new rules of the browser market in which Firefox no longer holds such a central location.

Firebug was dominant in the days when Mozilla's Firefox was the dominant challenger of Microsoft's Internet Explorer, but now the browser market is as competitive as it's ever been. Chrome is steadily gaining usage share at Firefox's expense. On top of that, the use of mobile browsers is exploding, and the scope of what people do with a browser has expanded tremendously.

Web programming is a hot area as the era of static Web pages gives way to the era of dynamic Web applications with animated elements, interactive user interfaces, and heavy-duty software written in the JavaScript language. That makes the task of creating developer tools harder.

Barton had been an IBM employee. IBM made Firefox its default browser a year ago, a major endorsement for the open-source browser, but evidently IBM's priorities don't extend as far as Firefox these days.

"I think our current drive to re-architect Firebug is on the right track, but I could not obtain another year of support from IBM to contribute to that work," Barton said.

Web developer tools in browsers are under rapid development as browser makers court Web programmers. Chrome has its suite of developer tools. Apple's Safari has its Web Inspector and other tools. IE has the F12 developer tools. Firefox has a developer tools group, too.

Firebug is an elaborate extension for Firefox. But it's been a lot of work at times to keep Firebug updated as new versions of Firefox arrived. That was the case two years ago when Mozilla was trying to turn the new-version crank faster, and it's even more the case now that Firefox is fully engaged in Mozilla's new rapid-release program for Firefox.

Thus, Barton described Firebug's present challenges:

Working on Firebug with this great group of contributors was fun and I believe we had a tremendous impact on the Web over the years when Firebug was the only decent Web debugger Now all of the browsers have (or will soon have) their own debuggers. Basing next gen work on Firebug is not practical. The pace of change in browsers is too fast for our team size. Firebug hasn't really been able to keep up with Firefox, let alone compete with other tools. Moreover, the shift from desktop to mobile and from one high-tech browser (Firefox) to three or more requires additional development effort."

Dion Almaer, who had worked on developer tools at Mozilla earlier in his career, noted the significance of Barton's new job in a blog post today.

"Firebug used to be the way you debugged your sites, but that is changed," Almaer said. "It is too early to claim that Firebug is zombied, but all eyes will be on that...especially as we see other browser tools continue to blossom."