hi Jdm2, the password for your firefox account is the only way to decrypt the sync data stored on mozilla's server. without knowing the correct password it won't be possible to retrieve that data.

Thanks! I see, Dammit!

OK, then will Firefox just let me continue to try out all the possible passwords i might have chosen indefinitely? (and will it let me open a 2nd concurrent sync account, just in case i never succeed?)

And/or...is there some way to recover my old sync data from my old machine? i have data stored on a sepearate drive from my OS. The data drive is intact, i hear. Whether it would have what i need or in reccoverable form, I don't know?

As you see I don't give easily. I've been using that sync account for Idon't know how many years, i don't know how many changes of machine. Given present problem, I don't know how the heck my sync account survived this long. You can practically rely on me to forget passwords.

Thart is, it looks to melike I must surely have gotten around this same problem before, somehow. Just can't recall how.

Thanks again :)

PS, I seem to have a memory of just giving up, some 5-6 years back, resetting passwork and then all my sync data miraculously flooded back in , against expectations. Was that just a dream? Or have they changed the system? or what? Obviously I wouldn't want to try it, just to find out.

the sync system worked differently back then - the data was encrypted with a particular sync key & as long you were in possession of that you could change the account credentials back and forth. now the account's password is used for this purpose: https://blog.mozilla.org/services/2014/04/30/firefox-syncs-new-security-model/

the place to look for relevant data on your old harddrive would be the firefox profile folder: Profiles - Where Firefox stores your bookmarks, passwords and other user data

Ohhh! thank you. Some really helpful , to-the-point replies here. (And I will definitely mark them as helpful, soon as I'm sure they won't close the thread on that account *chuckle* . I've been too enthusiastic too soon on some support boards. )

I can't look right now (PC stalled in repair shop indefinitely. Actually the PC isn't even old, nor damaged. It just won't update the new Windows installation. That's a known issue apparently, but the usual fix doesn't work, apparently) .

So, the million dollar question is: would that profile have survived the fresh windows installation? ( Looks very doubtful to me :S)

You can have as many Sync / Firefox Accounts as you have email addresses. But i your situation I can't see how it would help you now.

The correct procedure to perform prior to sending out that PC for repair would have been to backup your data, if that PC was operational. And if that PC was dead and you couldn't backup your data, the first step in the repair procedure should have been to have the service personnel backup your data for you, possibly via connecting your hard drive to another PC as a "slave drive".

Sync was never intended to be used on one device, in lieu of a proper backup. The first version of Sync that used the "3rd factor" for connecting to the Sync server was a problem for some users who didn't realize that "Sync key" was necessary; those users thought they only needed their email address (username) and the account Password. Well, Mozilla decided to "fix that issue" in Sync 1.5 by combining the encryption key into the process of creating the Account Password; so now the Password is the "key" to the stored data. Change the Account Password and the stored data can't be decrypted; thus is useless - so it is deleted to allow the user to key using that account. Plus that allows the user to clear their data from the Sync server when their Sync data is corrupted, by merely changing their Password.