Created attachment 55981 [details] screenshot of the submenu with Tiled backing store option dimmed run $ run-launcher --qt -graphicsbased -tiled-backing-store http://google.com on the terminal. GraphicsBased and Tiled backing stored are toggle one correctly, but the later can not be toggle off becaused Developer->QGraphicsView->Toggle Tiled Backing Store is dimmed see attached screenshot
more details: turning off QGraphicsWebView mode (Developer->QGraphicsView->Toggle use of QGraphicsView) and then back on , makes "Tiled Backing Store" menu work again
*** This bug has been marked as a duplicate of bug 39491 ***