Hi i sometimes want to move Opera out of the way quickly. On a Macbook Retina this means positioning the mouse into the 5pixel high strip above the tabs in order to grab the window. Inevitably I select a tab instead. This is painful and happens approximately 98% of the times I want to move a window. Wouldn't it increase ease-of-use to allow users to simply select a blank area of the webpage and drag the browser with that? Or have a large blank area in the tab bar for dragging windows?
On Linux, you can hold a modifier key to drag a window. Opera has to support drag for selection, I think a modifier key like Alt is the best you'll get.