To switch between normal / large icon sizes on all toolbars:

  1. Click on a toolbar menu button at the bottom-right hand side of every toolbar.
    Toolbar menu button screenshot
  2. Choose Add or Remove Buttons->Customise... menu item, then click the Options tab.
    Customize - Options dialogue box
  3. Click on Large Icons and your toolbars should then look something like this:
    Infix with large icons