If you are a Firefox user and have upgraded to Firefox 29 recently, you may have noticed that the Add-on bar no longer exists anywhere which was placed at the bottom of the browser in earlier versions of the Firefox. This Add-on bar no longer exists after Mozilla implemented the new UI in the browser. Mozilla has removed the Add-on bar in latest version and now places an Add-on's button in the main toolbar.
But many users won't like it there as it may result in over-crowding the navigation bar and hence, want the it back at same place at bottom of the browser.
Use the Add-on Bar Restorer to bring the Add-on bar back
To restore the the old-style Add-on bar, you need to install the "Addon Bar (restored)" add-on. Installing that add-on brings back your old style bar and places it at the bottom of the Firefox browser just as it was before.
Any features which were before you upgraded to latest version in the add-on bar, will be restored too. But if you want to add anything else or customise it, then you can do that by clicking the customize button.