I find it kind of disarming to overload not-typically-overloaded events like this though. I wonder if it'd be possible to let the right-click menu appear as normal, but background a div that pops up and give you the option of downloading the nicer logo files?
In Firefox you can untick "Allow scripts to Disable or replace context menus" (hidden under Preferences/Content/Enable Javasript/Advanced), which gives exactly the behaviour that you described. I assume other browsers have similar options.
That should be possible if you do not cancel the event bubble when the overlay is shown. I did not have time to inspect their code, but I assume they are canceling the event.
You're thinking of preventing the default action, not stopping propagation. (Event.preventDefault() vs. Event.stopPropagation() in modern browsers.) But you're right, if they handled the right-click and did not explicitly prevent the default action it would do both.
