Clicking on nautilus opens new window rather than opened ones [closed]
Solution 1:
Since shift-clicking did not work for me I searched and found another solution.
Workaround mentioned in the corresponding bug report: Scroll the mouse wheel on the Nautilus icon.
Solution 2:
I suggest you press shift key with clicking.
with shift key, you can open new window. and with wheel scrolling, you can switch opened instances without new window.
I think that it's very easy, and It's a function of Unity.
You can see the additional information at What are Unity's keyboard and mouse shortcuts?.