A few weeks ago Mozilla announced another initiative to get some more applications into the FirefoxOS Marketplace.
I had submitted a simple compass application early on in the Marketplace's life, but thought that this opportunity would be perfect to get an PhoneGap wrapped HTML application that I created for Android onto the marketplace, so I applied for a phone for app port deal. Within a couple days I recieved confirmation that I would be getting a developer preview phone from Mozilla, in exchange for my app port.
Now, I could have waited around until I received the phone to get started working, but with the FirefoxOS simulator available as a Firefox Add-On I set to work right away. I had previously submitted an application so I knew the general Firefox manifest format which is probably helpful. Once I had a Firefox app manifest being served (with the proper MIME type) from AppEngine I was ready to submit. I did however wait until I had a physical device to test and ensure it appeared and functioned as I expected.