Mozilla on Monday began rolling out its first major Firefox user interface (UI) change in more than three years, seeding early adopters of the "Nightly" build with the new "Australis" revamp.

Nightly builds are designed for preliminary testing, and as the name implies, are automatically updated each night to that day's edition. Firefox's Nightly builds are Mozilla's roughest-edged editions.

"[Australis] is the next iteration of the Firefox user interface," said Madhava Enros, the head of Firefox's user experience (UX) design team, in a Monday blog. "It's not quite finished, and it needs more polish, which is exactly why we're so eager to get it out to a wider set of the community."

Mozilla last refreshed the browser's UI with Firefox 4, which launched in March 2011. It has been working on the new UI since at least May 2012, when Enros first brought up the changes.

Australis, said Enros, is Mozilla's attempt to both streamline the browser's UI and standardize it across all platforms, ranging from the desktop -- where versions are available for Windows, OS X and Linux -- to mobile. Mozilla has a version of Firefox for Android and is working on a "Modern," or "Metro," app for Windows 8.1.

Most of the visual changes appear relatively subtle. Tabs, for example, are more rounded than in the current production edition, and inactive tabs fade deeper into the background.

Enros put that into design-speak. "One of the most noticeable changes is our tab shape. Ours is Firefoxy - organic, friendly, and fluid," he said. "Background tabs are visually de-emphasized, leaving a space that's uncluttered and calm, where it's quick and easy to see which tab is currently selected."

Other departures from the UI and UX include a new customization panel and a Chrome-like menu on the far right that displays icons representing commands such as print, save page and accessing the browser history and preferences.

One change, however, may be more disruptive. Australis has discarded the orange Firefox menu in Windows, an element which first popped up in Firefox 4. The Firefox menu condensed most commands formerly on the traditional Windows menu into a single-click destination.

And Firefox will retain the separate address and search fields at the top of the window, even though users can type search strings into both. Other major browsers, including Apple's Safari, Google's Chrome and Microsoft's Internet Explorer, have done away with a separate space for entering searches.

While Enros was enthusiastic about the Australis debut -- "That's the new Firefox -- beautiful, streamlined, and customizable," he wrote at the end of his post -- and most users who left comments were complementary, a few weren't happy.

"Fine, switching to Chrome now," said Dom Diesel. "If you force a Chrome-like design on me ... I can also use the real thing."

Others said they'd give the changes a chance. "It's a little heartbreaking to see the old UI go, but I'll give the new one a shot," said Tom Hunkapiller, a Missouri-based developer.

Australis is currently slated to appear in the production version of Firefox 28, which has a ship date of March 4, 2014, according to recent notes on Mozilla's website. At one point, Mozilla was shooting for Firefox 25, which launched near the end of October.

The Nightly build of Firefox for Windows, OS X and Linux can be downloaded from Mozilla's website.

The new Australis UI (bottom) omits the Firefox menu in Windows (orange in the top image) and fades all inactive tabs into the background.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed. His email address is gkeizer@computerworld.com.

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This story, "Mozilla Ushers in New Firefox UI" was originally published by Computerworld .