Go to settings>customize (which will be at the bottom) Click that and from there it will lead you to a page which shows all the icons that you do not have in your toolbar. Just click the star and drag it into your toolbar and you're ready to go.

Have a great day! -Jon

Try restore the default layout:

• Customize the menu or the 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

You can easily move items between the three locations that way, so be cautious with using the right-click context menu on a toolbar.

You should be able to drag items back to the Navigation toolbar in customize mode.

I had tried to drag it from the left pane, once I dragged it to right pane I was able to put it back. Thanks Jon.

No problem glad I could help!