If it has disappeared, either it is not selected to appear, or it is on the extreme right of the screen.
First Select View and Toolbars and see if there is a tick next to Address Bar. If there is, click it to remove the tick then do it again to put it back. If there is no tick click it once.
If that doesn't work go back to View, Toolbars and remove the ticks from all of the other ones and also from 'Lock Toolbars'. Then look at the top right hand side and you should see it there. Left click and hold on the left hand side of it and drag it back to where it belongs then back to view >toolbars and put the others back.