@mustaqahmed, @domenic, ok.... first shot at this. Let me know how it looks. See also my other comments in the relevant HTML bug.

Thanks @marcoscaceres

Should this consume user activation, or just observe it? That's probably a question for implementers and/or the working group?

I think because this predates the new user activation model in HTML, it's currently "transient". It's definitely transient in Gecko right now - but I think because of the modal nature the payment sheet, we should consume user activation.

@aestes, @danyao, @rsolomakhin... the problem we are solving is:

window.onclick = () => {
   // set up payment stuff...
   const pay = request.show();
   // Does this succeed or reject? i.e., did .show() "consume" the user activation.
   document.body.requestFullscreen();
}

I’ll add tests once we deal with consume.