Starting next year, on in March 2014, Mozilla is planning to bring the Australis user interface for all Firefox users with version 28 of the browser. While the Australis experience has an attractive look and a unified appearance on all supported platforms, it will reduce many customization features available in Firefox at this moment. For example, tabs will stick to the top and you will not be able to change their location. You will be unable to re-arrange buttons and the addons toolbar will also be gone. With Australis, the appearance of the Firefox browser will be more like Google Chrome's UI.
If you prefer the classic user interface over the new Australis appearance, let's see how to disable Australis in Firefox.