Links from apps like e-mail and documents (or a command line on Windows desktop) open in a new tab of a running Opera window with no option to set it otherwise. Lot of people do not use tabs, for instance I don't like them because primarily they can not be switched by Alt+Tab between other app windows and secondly I prefer to see the title of a page on taskbar.
I've read such settings had been implemented in the past (Advanced options) but now it's gone. I believe there are many users that would love to have it back as an option (not necessarily by default). This essential feature maybe preventing a lot of people from switching from Firefox to Opera. At least it does in my case. Thank you.