Mozilla has announced the availability of Firefox 11, a new version of the popular open source Web browser. The update brings several noteworthy new user-facing features and a number of technical improvements under the hood.

When Firefox 10 was released in January, the browser gained a new suite of tools for Web developers. Mozilla continued to work on the browser's integrated development tools and has issued several major improvements in Firefox 11. One of the most significant new tools for Web developers is a new Style Editor.

The editor has a two-pane view that allows users to browse all of the inline and external stylesheets associated with a Web page. The right-hand pane will display the selected stylesheet as plain text with syntax highlighting. When the user modifies the stylesheet, the changes will be reflected on the Web page as the user types.

The support for live editing is extremely useful for Web developers who want to interactively experiment with design changes. It's worth noting that the CSS inspector Mozilla introduced in Firefox 10 also similarly supports live editing. The characteristic that differentiates the new Style Editor? It shows the page's actual stylesheets as text rather than just a condensed table of properties. Users can save their modified stylesheets to the filesystem.

Another new feature for Web developers introduced in Firefox 11 is a tool that provides a 3D visualization of a page DOM. The underlying implementation is powered by WebGL, a standards-based JavaScript API for performing 3D rendering in an HTML5 canvas element. The new tool shows various page tags as a stack of blocks, making it easy to see the structure of the page's element hierarchy. The user can zoom and rotate the 3D shape.

The 3D visualization has been available in Firefox nightly builds for testing purposes for quite some time. The feature was originally intended to land in Firefox 10, but was pushed back to 11. It's a fantastic technical demonstration of how WebGL can be used for data visualization, but it's not really clear yet if it will help Web developers solve real-world problems.

The browser's networking stack has been improved with preliminary support for SPDY, a new alternative to the HTTP protocol that Google first proposed in 2009. SPDY offers some performance benefits over HTTP. SPDY isn't ready for production use yet in Firefox, but it's included for testing purposes. Users who want to enable the feature in Firefox 11 can turn it on by toggling the network.http.spdy.enabled property in about:config .

Mozilla's built-in synchronization service has been improved in Firefox 11. It can now automatically synchronize the user's add-ons between instances of the browser. Mozilla has also enhanced Firefox's import system so that it can migrate data in the user's browsing data, including bookmarks, history, and cookies, from Google's Chrome Web browser. Another minor user-facing change that landed in Firefox 11 is a subtle redesign of the media playback controls for HTML5 audio and video content.

Due to a security issue uncovered during the recent Pwn2Own contest, Mozilla initially considered delaying the release of Firefox 11 this week. Firefox engineering director Jonathan Nightingale wrote a blog post yesterday indicating that the release might have to be pushed back. He later issued an update explaining that the security bug had already been identified and fixed internally prior to being reporting during the contest. As such, they decided to proceed with releasing the current build.

Firefox 11 is available for download from Mozilla's website. It will be rolled out through the automated update system soon, but Mozilla is temporarily holding off on releasing the automated update to make sure that it won't conflict with anything in the monthly Windows update that Microsoft planned to issue today. For additional details about Firefox 11, you can refer to the official launch announcement.