Are you logging into Sync? If you reset the Sync password, that scrambles the encryption key and subsequently wipes all the encrypted data in the cloud (or at the very least renders it inaccessible).

The login timeout could be triggered by an excessive number of attempts (usually the case, automatic attempts to Sync may contribute) or there could be a network interruption or server overload going on. The only thing to do in case of a timeout is to wait it out - there's no override that I know of, and one would make the timeout kind of pointless.

Fred knows more about these things than me, and his answer at https://support.mozilla.org/en-US/questions/1117723 says the lockdown may last a day or so.

What you can do manually is log out of Sync in Firefox so it doesn't try to connect automatically. Sync also uses local cache to an extent, as demonstrated in the support article, https://support.mozilla.org/en-US/kb/firefox-sync-troubleshooting-and-tips#w_firefox-sync-shows-a-cookies-are-still-disabled-error-message, so you could empty your cache and cookies as well in case they've gone bad: https://support.mozilla.org/en-US/kb/how-clear-firefox-cache.

Note that if you remove all cookies, you will have to log in again on sites like Youtube that use local cookies to keep your session alive.

... that doesn't explain why I get the same thing when trying a new account at a new email address that's never been near Firefox before. Signed in on the laptop, then on the phone and bam... same message as before.

I think I'm going to give up...

....and I tried it with a third email address.

Thanks for your help. I'm back to Chrome and a different solution.

Alright, best of luck.

See also:

• https://blog.mozilla.org/services/2016/04/09/stolen-passwords-used-to-break-into-firefox-accounts/

Similar to your situation, I attempted to log in (at accounts.firefox.com) a few times, finally decided to reset my password, then logged in. I soon logged out, but then decided that I needed to log back in. When I tried to log back in, I wasn't told whether my password was correct, only that I had exceeded my attempt limit. (I found something else to do for a few hours before trying to log in again, which was then successful.)

Obviously the act of logging in does not reset the failed attempts counter, which is ridiculously moronic. The attempt counter must be tied to the user's IP address, or else pranksters could remotely lock other people's accounts by intentionally failing attempts to log into said accounts, so there's no good reason to not reset this counter when a user successfully logs in.

So JeremyWW, because you failed multiple log-in attempts (on multiple accounts no less), Mozilla temporarily flagged you as a potential hacker trying to gain access via brute force guessing. See howsecureismypassword.net to see how quickly instant query hacking can work.