How to escape modal dialog in Safari? A certain Safari tab is asking for a username/password that I do not have.  I can click "Cancel" on the authentication dialog but it immediately pops up again.  The dialog is modal, meaning that it disables all other UI elements of the window except the minimize/resize buttons.

How can I close the problematic tab without quitting the application?
Open Activity Monitor, look for the process corresponding to the tab and quit it.