For anyone who wants to get ahead of the pack, Firefox 21 for Windows, Mac, and Linux can now be downloaded. The official launch will take place shortly and the new version will then be automatically pushed out to current users.

While we’re still waiting for the official change log, the details in the beta show several improvements to the developer aspects of Firefox.

The most obvious improvement is the ability to profile remote devices using your desktop version of Firefox. The way this works is that you can make a connection to a remote device such as an Android or Firefox phone, and so long as the user on the remote device accepts the connection, you’ll be able to see the profile of the remote instance in a separate Developer Tools window.

The Firefox Developer Tools window gained a new unified interface in December with multiple tabs.

In a blog post about the new feature, Anton Koyalyov of the Mozilla development team said:

"[It]part of our bigger effort to make sure that developers have the same high quality tools when developing mobile web apps as well as their desktop counterparts.”

Another developer improvement comes with the integration of the Add-on SDK loader and API libraries into Firefox. This removes the necessity of packaging them inside each add-on. In a post on the Add-ons blog, Jorge Villalobos, Add-ons Developer Relations Lead for Mozilla, said the new release also splits platform and app resources up so that they can be loaded individually. XBL Scopes are also now enabled, which could cause problems if you insert XBL bindings into content pages as calling functions to/from chrome can break under some circumstances and require additional code.

A full description of more minor developer changes is available on the Mozilla Developer Network site, though the document is currently marked as requiring an editorial review to add more features once Firefox 21 is launched.