Do you mean the arrow (gray when the list is empty, blue when downloads are on the list) that normally appears on the main toolbar?

Definitely it should be back after a Refresh, but you also can check the following:

(1) Use the Customize feature to search for an out-of-place icon or add it back from the box of unused icons. See:

Customize Firefox controls, buttons and toolbars

Note: The "Restore defaults" button at the bottom of the Customize tab resets your toolbar layout, but doesn't do a full Refresh.

(2) Check for possibly conflicting extensions. Test in Firefox's Safe Mode, which temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

Note that 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

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