My thinking is that many developers will build their mobile apps starting with just Firefox (and the Responsive Design View). Once they really start digging in to some of the APIs that exist in B2G but not yet in Firefox, they'll switch to the Simulator.

There are some differences between B2G Desktop (used by the Simulator) and Firefox today, not to mention the ability to check out Gaia (the user interface of B2G). My hope is that everything needed for the Simulator will roll into Firefox at some point.

I know you were likely kidding, but I thought I'd try to clarify where the Simulator fits in the development process for people building targeting Firefox OS.

(I'm the product manager for the Simulator, among other things)

I don't know if you're serious or not but I'll give you a nudge in the right direction for finding out what Firefox OS is: http://www.mozilla.org/en-US/firefoxos/