Before Firefox 4, the menu items for the browser – such as File, Edit, View, History and more were all over the place. After Firefox 4 was released though, Mozilla simplified the menu toolbar and dumped everything under the Firefox button. What if you want things to be even more compact than that? Then you need to pick up Compact Menu 2.
This simple add-on for Firefox will give you the old menu bar layout under a single button – so you can kind of mix the best of the old and the new when it comes to using Firefox 4. It adds a compact menu button to the navigation toolbar and then hides the big Firefox button.
You can fully customize the compact menu by right-clicking on the new toolbar button and selecting "Customize". From here you can drag the menu button to a new location inside of the Firefox navigation layout.
While there are other add-ons that will do the same job – I think Compact Menu 2 might do it the best. You can pick it up from the Firefox Add-ons website.