Try right-clicking on one of the toolbars, that will display a list of toolbars with a tick next to ones that are displayed. If you click on the name of a toolbar it will toggle displaying it.

You can also access this by selecting the View menu and then Toolbars.

If the above does not help, see back and forward or other toolbar items are missing, in particular the section on how to reset toolbars and controls.

You write I can see the second toolbar with 'most visited' getting started,' etc.

That sounds like the Bookmarks Toolbar with the default Bookmarks on it.

You also write But the third tool bar that has 'bookmarks' has disappeared.

Is that a toolbar added by an extension? Because you seem to see all three default Firefox toolbar (Menu bar, Navigation Toolbar, Bookmarks Toolbar).

See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems