The main advantage of using a drop-down menu is all the space it frees up, letting you get a better view of the content on the page.
Instead of the menu bar, there will be a new button that, when clicked, will show you all the options that were previously there. Although this menu is in a drop-drop style, it will still work the same as before.
You can also hide whatever menu elements you want. So if you don't want to see the 'help' option, for example, you can choose to hide it in the add-on's settings.
To make the menu bar look like the image, just drag all of the icons to the navigation bar. When the last one is empty, hide it.
This version is compatible with Firefox 1.5 and 2.0