Mozilla clarifies that its planned overhaul of Firefox’s interface will be pushed back to Firefox 4.0, whose major release now will be shipped before the end of 2010. Mozilla previously said it would redesign the look and feel of its open-source browser in a two-step process, with part of the redesign debuting in Firefox 3.7 — a minor refresh scheduled for late in the first quarter of next year — with the rest following in version 4.0.

Mozilla’s interface plans, particularly those intended for Firefox for Windows, have attracted attention because the company last September said it would "ribbonize" the browser by borrowing graphics concepts from Microsoft’s Windows 7 and Office 2007. Users blasted the idea. Later, Mozilla clarified its intentions, saying that although it was going to eliminate the traditional top-of-the-frame menus in Firefox, it was not going to turn its browser into a graphical doppelganger of Office 2007. Mozilla’s newest plans for Firefox 4.0 center around a so-called "App Button" that will take the place of the menus long-seen in Windows applications, said Stephen Horlander, a designer and longtime contributor to Firefox’s interface.

The Firefox button in the mockup above is the App button that leads to all the menus that are usually found in the menu bar of Firefox 3. Some users might argue that it is a waste of space to put the app button in single toolbar instead of placing it into an existing toolbar. The removal of the title bar would have barely any effect on the available screen estate otherwise.

A visual comparison between the latest Firefox 4 mockup and the current Firefox 3 design shows that the developers aim at reducing the header area of Firefox by 40-50%.

Additional changes in the mockups include:

• Refining Toolbar Button Appearance: Some initial work has gone into making the toolbar buttons more visible on light backgrounds and more crisp and dimensional (pressable).
• Location Bar: Created some very early visuals for reevaluating site identity. Also the location bar is now properly recessed instead of floating.
• Retain Separate Search Bar: With the LocationBar containing an increasing amount of functionality it may be best to retain a clear distinction between the two fields.
• Bookmarks Widget: On a default profile or existing profile that hasn’t modified the Bookmarks Toolbar it will be hidden by default and the Bookmarks Widget placed in the Navigation Toolbar.