So many people on HN coming up with elaborate ways to get a consistent UX that works for all cases. In my mind the best thing to do would be showing the lightbox but also not disabling the context menu.

Advantages:

    * Shows context menu immediately, allowing for edge cases
    * Shows lightbox
    * Always consistent, no clearing cookies or preferences to get it back
    * Unobtrusive; "don't make me think"
    * Simple to implement (just allow the event to propagate)
    * Robust, context menu works if lightbox breaks