Comment 4 for bug 1546677

A Popover is closed automatically if you click outside of it. Esc and outside click is basically the same thing. In any other circumstances it is the developer who closes it, for instance when an action is selected. So there shouldn't be any difference between handling Esc or outside click. Any other closing case can be captured by the actions assigned to close the Popover.

I see the Browser's bookmarking popover has a Cancel action on the bottom. This is pretty confusing as Popovers are not Dialogs, which would need an explicit action on their layout to be able to close - Esc or outside click does the job.

But really, what si the use case you need to know the Popover was dismissed?