If you press the Firefox menu button and select Customize, you can drag the reload button back to the toolbar. See Customize Firefox controls, buttons and toolbars for more information.

Hope this helps.

When I go to the link above, it does not have the refresh icon to drag to the toolbar.......

Open the Customize window and set what toolbars (Show/Hide Toolbars) and toolbar items to display.

• 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/en-US/kb/customize-firefox-controls-buttons-and-toolbars