Hello Linux Geeksters. As you may already know, the Mozilla developers have been working hard in the last year, in order to get the new browser theme, called Australis, ready for release. Australis has a modern and simplistic look with monochrome icons, rounded tabs, bookmarks, download panel, all together providing a Chrome-like eye experience. See the above screenshot for more information.
Australis was included in the Firefox 28.x Nightly version and so, all the users using that version were forced to use the new interface.
Because many Firefox enthusiasts were not happy with the new theme, since it is very similar to the Google Chrome interface, the Mozilla developers hace created a new branch of Firefox 28.x Nightly called Holly, which comes with the normal interface, and not Australis.
Since Australis is not ready until the 9th of December when Firefox 28 is scheduled for release, the developers aim to set it as default in Firefox 29 Aurora. It will be available again, in the Nightly version of Firefox 29.