Because one of the main Firebug authors started working for Google, on Chrome, and even he thought Firebug wasn't the best platform to keep innovating on: http:

Because one of the main Firebug authors started working for Google, on Chrome, and even he thought Firebug wasn't the best platform to keep innovating on: http://news.cnet.com/8301-30685_3-20080338-264/firefox-world-loses-web-dev-guru-to-chrome/ http://news.cnet.com/8301-30685_3-20080338-264/firefox-world... http://blog.mozilla.com/devtools/2011/05/25/the-relationship-between-firebug-and-mozilla-developer-tools/ http://blog.mozilla.com/devtools/2011/05/25/the-relationship... What I gather from that is that they will keep developing and improving Firebug (or rather, support it, because Firebug authors aren't from Mozilla), but that they also want to experiment with other devtools that are hard to implement in the existing Firebug codebase. The devtools are also one of those new things that are now rapidly improving from release to release, so they're bound to have "version 0.9" issues. Why couldn't they instead focus on making Firebug better and providing a better, deeper integration between Firefox and Firebug? I was always under the impression Firefox plugins can do anything they want and have complete access to all the API. And that this is exactly why they tend to a) be more powerful than the equivalents for other browsers b) have more compatibility issues.