Yes, through the browser is good... but what is needed is a sort of 'inter-provider' agreement between the large players (similar to some interbank systems like ClearXChange)...
Which would create this core clearing house... so that the soliciting interest because of the agreements with those providers could offer its button through all browsers simultaneously.
I also believe that such an agreement would place tremendous pressure on the various payment vehicles to join this network... rather than trying to do micropayments by themselves. (similarly with email providers)