Mozilla last week said that the earliest its new "Australis" user interface (UI) will appear in Firefox is at the end of April, six weeks later than the company previously projected.

Australis, the first visual overhaul of Firefox since March 2011, will be promoted to the "Aurora" channel today as the company rolls out Firefox 29 to its pre-beta build line. Mozilla uses a three-stage development process that ships Aurora, Beta and Release versions of each version of Firefox, with six weeks separating Aurora and Beta, another six between Beta and Release.

[See also: A slideshow tour of the UI changes in the latest Firefox Nightly build.]

That means Mozilla will offer Australis to the Release channel -- the build most users run -- on April 28 at the earliest. It's also possible that the open-source developer will push Australis even further into the future.

Australis 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 continues to plug away at a "Modern," or "Metro," app for Windows 8.1. Many of Australis' visual changes are subtle, with more rounded tabs, inactive tabs that fade deeper into the background and a revamped customization panel. Australis also dumps the orange-colored Firefox menu in Windows, an element which first popped up in Firefox 4.

Mozilla has touted the UI refresh as "organic, friendly, and fluid," the last word one that also rolled off Microsoft executives' tongues early in the development of Windows 8.

"Upon the following uplift (March 17), we'll again make an evaluation on uplifting Australis to Beta or holding it back on Aurora for the Firefox 30 train," said Justin Dolske, a Mozilla senior engineering manager, in a note to a planning discussion forum. "There is significant risk to backing out a large project from Beta, so the intent will be to ride a Beta to Release."

If Australis doesn't release in April with Firefox 29, its next shot will be Firefox 30, scheduled to ship June 9.

"Significant development will continue over the next six weeks, as we burn down current Australis bugs as well as new issues found by the Aurora audience," Dolske said.

While Mozilla proceeded with the Australis look-and-feel, some Firefox users continued to criticize the changes.

"If I want something that works Like Australis I'll use Chrome," said Phillip Jones in a message last week on the same planning forum. "The day it hits the regular channel is the day I run Time Machine, put back the old, and shut off updating Firefox."

In response, another user pointed to a Firefox add-on, Classic Theme Restorer, that can return an Australis-equipped Firefox to the older 2011-2014 UI, including restoring the orange menu button.

The Aurora 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. Users who detest the new look can install an add-on that restores the UI to its old glory.

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

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