When I click "send me instructions" on the iPhone and put in my email address, I get the message "Unable to submit your email, please try again later (400)." I've been getting this for a week.
When I try to set up an account on my desktop, I click "Finish" and the dialog box disappears but nothing else happens. I still have "Set up sync" in Tools, nothing happens if I click "I have an account". Nothing happens if I click "Sync Options" either.
First you need to set up Firefox Sync in your computer. If you are seeing "Set up Sync" in your computer is because it's not set up. If you already created an account you need to reset it, if not, that's the first thing to do.