If you click, it's a tab. If you drag, it's a window. What's so difficult about that? There's no reason to click on a window that is already fullscreen, anyway.

If you click, it's a tab. If you drag, it's a window. What's so difficult about that? There's no reason to click on a window that is already fullscreen, anyway. (OP's problem only occurs if the browser is fullscreen.)