Firefox is getting a major redesign, codenamed Australis. Of course, Firefox has been "getting" this redesign since 2011 and Mozilla doesn't seem that much closer to bringing it to fruition.
In fact, the only visible change that is the result, an indirect result at that, of the Australis project is the download panel which has only been enabled by default in Aurora very recently.
But Mozilla is working on it, one of the more interesting things it's doing with the redesign is a new menu and a new UI customization tool.
Firefox with Australis will have a menu button and a pop-up menu very similar to Chrome's existing one.
However, the menu itself will be quite different than anything we've seen in a browser before. While the design is not final, it's looking rather interesting.
Even more interesting are the customization options. Users will be able to add and remove items from the main menu as well as customize the main toolbar in any way they see fit.
The customization tool is not ready, but you can check out an interactive mockup here. In the mockup, you'll be able to play with the menu and the customization page.
The customization tool seems simple to use but quite powerful, you'll be able to add shortcuts to any item you use often, bookmarks, developer tools and so on, either to the menu or the toolbar itself.
Nothing is set in stone, apart from the unified address bar/search box, the back button and the menu button. There are some very experimental builds of Firefox, for Windows and Mac, with the customization tools, incomplete as they are now, but they're really not recommended for everyday use.
All that said, there are many good ideas in Australis, but until it actually becomes a part of Firefox they are just that, good ideas. Still, Australis, or at least parts of it, should be landing sometime this year.