Who has liability when a user of mine says their account got hacked? The email provider? My site? Mozilla?
If one of my users has $100 go missing from their account, then they are going to expect me to replace it, not the email provider, not mozilla. I don't like the idea of shifting security to a outside platform, because I still retain all the liability when things go bad, and they always will (key loggers, spyware...)
Sites that deal with financial transactions will be reluctant to adopt this for sure.