Mozilla has officially released Firefox 10. The new version of the open source Web browser includes a handful of improvements and new features. The browser's built-in tools for Web developers got a particularly significant boost in this release. The new version also offers better support for a number of Web standards.

Firefox's developers decided last year to transition the browser to a time-based, six-week release cycle. The new release management strategy ensures that performance improvements and support for new Web standards reach users as soon as possible. The faster release cycle posed challenges, however, for enterprise adopters and other users who require a longer a longer support period. In order to address that issue, Mozilla has decided to offer an annual extended support release with a full year of updates. Firefox 10 is the first official extended support release.

A minor adjustment to the browser's navigation bar is the biggest user-facing change in Firefox 10. The forward arrow button is no longer persistently visible by default in the navigation toolbar. It will only appear when the user navigates back a page. That means the button only shows when it can be activated. When the user clicks the forward arrow button and returns to the front of the history stack, the button will disappear again.

The distinctive keyhole shape that is formed by the back and forward buttons in Firefox's navigation toolbar has been characterized in the past by Mozilla designers as an important part of the browser's visual identity. Much like the angular tabs in Chrome, it's an aesthetic characteristic that is uniform across platforms and helps make the browser recognizable.

The user interface change in Firefox 10 will make it so that the keyhole shape is only visible when the user navigates back. The feature worked predictably in our tests and didn't pose any problems in practice. It's worth noting, however, that it doesn't appear to be available when the user has toggled the preference for small toolbar icons.

Another major change in Firefox 10 is the introduction of new developer tools. Previous versions of the browser have included a Web console, a JavaScript scratchpad, and a simple tool for inspecting the Document Object Model (DOM). Firefox 10 has a new tightly-integrated developer panel with a richer DOM inspector and a tool for viewing, toggling, and modifying CSS properties.

The DOM inspector follows your cursor as you move it over elements of the page and will lock in on an element when you click. An HTML pane at the bottom of the screen will show you the markup for the target element and allow you to modify the values of element attributes. The HTML inspector pane also has a slick breadcrumb bar that makes it easy to see the position of the target element in the page hierarchy.

The CSS inspector will show you a list of CSS properties associated with the selected element, including inherited properties. Each one has a checkbox that you can click to toggle visibility. You can also click one of the values to replace it on the fly.

These built-in development tools in Firefox are simpler and less intrusive than more sophisticated alternatives such as the Firebug add-on. There are a number of additional features under development that will be included in the inspector panels in future versions of the Web browser. One of the most intriguing is a tool that uses WebGL to show the user a three-dimensional representation of the page DOM. That feature wasn't ready for inclusion in Firefox 10 and will potentially appear in the next major release.

In addition to the new inspector, Web developers can also look forward to improved support for Web standards. An addition of particular significance is a new full-screen API, which makes it possible for an individual HTML element to break out of the browser window and stretch itself to cover the entire screen. This feature is going to be especially useful for videos and games. You can see it in action by visiting Mozilla's fullscreen demo page.

We first wrote about the full-screen API in November, when the feature originally landed in nightly builds. Mozilla carefully considered potential abuse scenarios when implementing the feature. It's designed so that an element can only switch into fullscreen mode in response to a direct user action. The browser ensures this by using a technique similar to the one used to block unwanted popup windows.

Another addition in this release is support for 3D CSS transforms. This feature, which was originally created by Apple, offers a declarative mechanism for applying animated three dimensional transformations to individual HTML page elements. It's important to note that 3D CSS transforms are entirely distinct from WebGL, which is a low-level JavaScript API for 3D programming.

Support for 3D CSS transformations is a welcome addition to the browser. Developers are already using the feature in the wild, but most of the existing 3D CSS content was authored with WebKit-specific prefixes and consequently won't work in Firefox yet.

Firefox 10 is a solid release that expands the browser's capabilities. Although the lineup of new features is slim, it's a respectable update by the standards of the rapid release model. The new version will be pushed out through the Firefox update system shortly. Firefox 10 can also be downloaded directly from the Mozilla website. For more details, you can refer to the official release notes.