You can open the Opera Menu left top by clicking on the most top left pixel, but you can't close the same menu with the same pixel.
Also, when you want to open a new tab you gotta click rather precise on the + next to existing tabs. If you click all on the top (which works in Firefox) nothing happens:
If you move your mouse cursor 3px lower you can open it:
If you compare that to Firefox:
you can see that it requires way less precise mouse targeting to trigger the + new tab button, which is prefered.