Do what?
Tabs are always above the Address bar. Am I just misunderstanding?
Maybe he means the bookmarks tool bar?
For a longtime user like myself, tabs were originally below the menu and address bars, clean and easily seen. Firefox decided to follow other browsers and put them on top, but those who enjoyed them on the bottom have to resort to adding steps in the userchrome.css file to get them where they belong. It’s been relatively easy for a programmer to achieve but for us users, especially an old or older one like myself, it’s more daunting and help is needed.