If you're including me there, sorry.  I can try another explanation or answer some questions?  (But my IRL-lag may be high.)

I don't think bitcoind needs to be running.  The mimetype has an app to handle it, call it bitcoin_pay_gui (or plain bitcoin with some option flags).  When this starts it needs to check for a running bitcoin(d) and talk to it, else start one or do the operation itself.

To make the payment, ideally you have the latest block so you know your balance (yes?) but in cavalier mode you could issue the transaction on old money without checking you still own it.

Then the app should probably hang around to see some confirmation, or failures, and notify the user.  After this it can quit if nobody needs it.



Hmm, if the browser says it Accepts:application/bitcoin-payment-request then mybitcoin.com is irrelevant, but if it doesn't (very likely) then it's certainly worth putting a suitable link in the "page you get before it just gives you a file you can't yet deal with".  I'm not sure this is what Accepts: was intended for...

Presumably mybitcoin.com could usefully fetch & process this mimetype?  This seems less useful than a multi-format spec of standard keys & values to send when requesting payment from someone..?