Oh, yes! I have the same matter. Firefox as well is true portable. Also the Passwords migrate with the USB Key and not remain nothing else in the PC. In my point of view, Google and Opera strategies to save the password in the PC is almost dangerous and leak of security. In the PC is hacked also the browser is hacked. Otherwise with the master password (Firefox) i can protect very personal data.
I Hope that Opera give us a Choice to use a password strategy. For most users thats belong to guided choice. For me is use or not use Opera. My Wish is to select.