Right-click on a toolbar and select Customize. You can then drag and drop the buttons and place them where you want.

For more details on this see https://support.mozilla.com/kb/How+to+customize+the+toolbar

Thanks so much, Tony. I had tried Customize, but gave-up when I didn't see the Reload and Stop icons in that menu. I'd also tried dragging them without having the Customize menu launched---and of course, that didn't work either. Dragging them from place-to-place in my toolbar with the Customize menu on-screen worked like a charm!