You can add it. Just keep the proper hierarchy: Keybindings -> Basic -> OpenWindow, and don't forget about commas. If there's an error, Preferences will be renamed to Preferences.bad.

I added the line "OpenWindow": true,
after "browser": {

No results

My problem is that after opening new window the focus is still on old window,
not on new window.

Thanks, I've found preference file, but there are no words "OpenWindow" or "window" ...

Firefox irritates me since it does not switch focus to new opening window.
Well, I have installed last opera v 22.
I can't find advanced settings, where I hope I can set opening new windows
instead of new tab.
I marked checkbox "Show advanced settings".
But where they are?
They is only "settings" in menu.
No choice to select any other settings in menu.
No popup menu when I focus mouse on the "settings" line in main menu.
Maybe it was eliminated in new version,
because I googled pictures where advanced settings existed before.