Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. Is the problem still there?

Type about:customizing<enter> in the address bar. Look for Show / Hide Toolbars at the bottom left.

There is also a Restore Defaults button at the bottom middle.

You may have removed the button(s) from the Navigation Toolbar by accident.

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

Open the Customize window and set which toolbar items to display.

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

See also:

• https://support.mozilla.org/kb/customize-firefox-controls-buttons-and-toolbars