Please update to Firefox 29.0. Firefox has transitioned from using sync to using Firefox Accounts. Upon installing 29.0, visit about:accounts in the URL bar to get started with setting up an account for synchronization.

Thanks. It turns out I got my new computer at the exact time that FF dramatically changed their sync system. There was never a previous email or username or password, so the sign in page was misleading. Many users reading this will have to create an account, upgrade all their synced computers, unsync them, then sign in to their new FF accounts. Syncing will happen automatically.

The problem with "automatic" syncing was illustrated by my experience. Instead of syncing on the computer I wanted to copy, it synced from the computer I wanted to change. So, all my computers got all the bad passwords and duplicates of many good ones. It took a long time to straighten that out. But I made the changes on one computer and that changed the others. And new changes will automatically update. So it's an "easier" system. Still, I wish there was a way to choose when to sync. But thanks for the help anyway.