Try this. https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars

The Library button and the Home button are no longer present by default on the Navigation Toolbar, you need to drag them out of the Customize palette to the toolbar.

Right-click one of the existing icons next to the Search/URL bar and then click 'Customise toolbar.' That will then show all the ones available and you can drag ones that aren't normally visible to where you want and drag ones away that you don't use.