Note: You must click somewhere in this page for the OnBeforeUnload dialog to fire when you Navigate somewhere else.
Subframe from webdbg.com
crbug.com/1065085 - block cross-origin dialogs
Try clicking in this page, then create five or six new tabs to example.com, CTRL+TAB through them rapidly, then click the red X to try to close the browser with this tab in the background. Does this tab repaint behind the beforeunload confirmation prompt?
