Tabbed browsing in Firefox 4.0 - How Firefox 4.0 may look
Look at how the tabs are positioned below the address bar in this screenshot. Firefox could possibly add a bookmarks widget as an upfront replacement for the bookmarks menu/bookmarks toolbar, leaving the option to turn those on.
Do you prefer browser tabs above or below the address bar? Software developers at Mozilla Foundation are trying both.
They are also looking at how to give users more feedback on what the browser is doing when the user types in a URL to go to a website.
These sceen shots show what the Firefox developers are looking at for version 4.0.