Click-ons on top of Firefox page are gone

Just right-click anywhere on the navigation bar (the one with the forward and back buttons) or the standard toolbar with File, Edit, etc. and select Customize. You can then look through the available buttons and drag-and-drop them where you want them. You can also remove buttons the same way, dragging-and-dropping them into that window. There is also a "reset default set" button there so you can restore all of the buttons which were originally present.

Note, however, that a corrupted file in your Firefox profile can also cause this. Thus, while the above solution usually resolves the problem you may have to do a little more work if the problem keeps returning.

Let us know.
John