Desde las páginas de ayuda de Opera:
Personalizar barras de herramientas
Puede cambiar la apariencia de una barra de herramientas agregando elementos, cambiando dónde o cuándo se muestra, cambiando el estilo y el ajuste, o volviendo a sus valores predeterminados. Para hacer esto, presione Ctrl + clic en la barra de herramientas y selecciona "Personalizar". La barra de herramientas está resaltada con un borde amarillo y puede comenzar a personalizar la barra de herramientas de las siguientes maneras:
To add an item, such as a button or search field, select "Appearance" and in the resulting dialog, click "Buttons" and drag a new button from the list for any toolbar to the highlighted toolbar.
To change where the toolbar displays in the browser, select "Appearance" and change the Placement setting.
To change the style of the toolbar, for example, to use text rather than buttons or images, select "Appearance" and change the Style setting.
To change the wrapping of the toolbar, select "Appearance" and change the Wrapping setting.
To set the toolbar to display only when it is needed, select "Appearance" and check "Show only when needed". This is especially useful for the navigation bar.
To undo any changes you made and reset a toolbar to the default setting, select "Reset Toolbar to Its Defaults".
To remove an item from a toolbar, select "Remove from Toolbar".
To change the order in which toolbar buttons or icons appear, drag-and-drop the buttons or icons.
To change the size of the buttons on all toolbars, select Tools > Appearance > Skin and in the "Icon Size" field, select the percentage to scale the buttons.