This is a useless complication. Making the button customizable like every other button, with the same size of every other button (it's not clear why it should be different) and allowing to place it outside the urlbar, would be by far better. Keep in count that is one of the most used button in the interface so let the users place it where they want, don't force people to use elements in a obligate way, in particular when the choice is highly debatable (and Australis has too many debatable choices to include even this one). Forcing the users to search for an addon only for moving a button in the interface it's a nonsense.