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

• Right-click empty toolbar area -> Customize
• "3-bar" menu button -> Customize
• View -> Toolbars
  *you can tap the Alt key or press the F10 key to show the hidden Menu Bar temporarily

• 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.

See also:

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

cor-el, your reply is worse than useless. I tried clicking "restore defaults" and it reset the customizations I did without solving anything, so I wasted time putting things back.

Anyway, can anyone actually respond to the question, instead of copying/pasting useless canned replies?

What happened to the open new tab button?

There is an Undo button available when you click the Restore Defaults button that you could have used to immediately restore your customization.

Note that in customize mode the plus button is at the at the right end of the Tab bar. If you close customize mode then the plus button should move to a position right after the last tab. Customize mode should have restored the plus button. If this didn't happen then try to reset the browser.uiCustomization.state pref on the about:config page. Make a backup of the current value in case you want to restore the layout. To make this work properly you need to close and restart Firefox after you have reset the value or have pasted the saved value back in the pref.

cor-el said

Note that in customize mode the plus button is at the at the right end of the Tab bar.

Ahhh okay thank you very much for that!