How to re-enable bookmark deletion confirmation in Calibre e-book viewer?

Whenever I deleted a bookmark in the Calibre e-book viewer, a confirmation window used to pop up. That window had an option to disable further confirmations, and I chose to disable it some time ago. Now I’d like to re-enable it, but I can’t find a way. I checked the reader preferences but didn’t see anything related to restoring the dialog.

Does anyone know how to turn the confirmation window back on?