@howbizarre, @mbedni , @ivanmca , I have the same problem in Opera for Windows (not reproducible in Opera for Mac). Reproducible stable, each time after relogin DevTools overlaps my page and window.innerWidth is incorrect as there are no DevTools. It reproduces for Left, Right and Bottom positiones of DevTools. Only when I resize the window manually it recalculates width correctly with according to DevTools width. I tried resizing programatically but it didn't help