Firefox 4 tabs are placed above the browser’s address bar by default. While some users might like it, some others might not and prefer to have the tabs on the old position, which is below address bar or below the bookmark toolbar. This, however, can be done quickly and easily.
To move tabs from top to old position in Firefox 4, click the Firefox small, orange button. Then select “Customize’ and click “Tabs on Top” to remove the check mark. That’s it. You’ll see that the tab position is moved below the address bar.