Actually, there are some other ways you can do it. But first, you could check whether the bookmark buttons are available to add back to the toolbar, or if they have "overflowed" due to an overly full toolbar.

If your toolbar has an icon similar to >> check that overflow list for the missing buttons. You can move them using the Customize feature. See: Customize Firefox controls, buttons and toolbars.

If they are nowhere to be seen, you also can use the Customize feature to check for them among the available controls to be added to the toolbar.

And here are some other ways to create a new bookmark:

• Ctrl+d
• right-click a blank area of the page > Bookmark This Page
• (classic menu bar) Bookmarks > Bookmark This Page

Note: if you do not ordinarily display the menu bar, you can show it temporarily by tapping either the Alt key or the F10 key.

Note that you may have accidentally removed button(s) from the Navigation Toolbar.

If you right-click a toolbar item in normal (non-customize) mode then you can remove this item from the toolbar.

• "Remove from Toolbar" will remove this item from the Navigation Toolbar and moves it to the Customize palette ("3-bar" Firefox menu button > Customize)
• "Move to Menu" will move this item to the "3-bar" Firefox menu button drop-down list
• "Move to Toolbar" in the "3-bar" Firefox menu button drop-down list will move this item to the toolbar

• if missing items are in the Customize palette then drag them back from the Customize window to the toolbar
• if you do not see an item on a toolbar and in the Customize palette then click the Restore Defaults button in the Customize palette window to restore the default toolbar set.

• https://support.mozilla.org/kb/navigation-buttons-missing

Thank you, Cor-El. Your explanation was exactly at my level of understanding, and not only is the problem solved, but now I know how to solve other problems with the Navigation Toolbar (and now I even know that this is its name!).