Mozilla Firefox version 4 has a look similar to Google Chrome with tabs being shown on top by default. But you can toggle if you want to see the tabs on the top of the window or below the navigation bar. Here is how :
- Open your Firefox browser.
- Click on the orange colored Firefox button on the top-left.
- From the menu select Customize → Tabs on Top as shown :
- The tabs would be shown below the navigation bar if you un-check the Tabs on Top option. If you check this option, then tabs would be shown on top of the Firefox window.