Marketplace/PaymentPolyfill
From MozillaWiki
What is it
A library to provide limited navigator.mozPay() and window.mozPaymentProvider functionality to browsers that don't support mozPay. It means that developers will have *less reason not to use* Marketplace payments.
How it works
Presumably this will be added to fxpay?
https://bugzilla.mozilla.org/show_bug.cgi?id=1044219
Supported browsers
Persona did a similar thing, their list of supported browsers was:
https://developer.mozilla.org/en-US/Persona/Browser_compatibility