Then you need to log off all sync account for both users and then go to Firefox browser and delete the data/login so they don't show up. And then make separate OS user accounts that has their own login and pswd to separate the browser sync data. If you keep sharing the same account and Firefox browser this will keep happening over and over again. You need to make separate if Windows OS separate accounts to keep Firefox browser data from another user Mozilla to the Firefox again.

Hmm, I don't think it is possible to easily detangle the data. Probably it requires manual cleanup or restoring from a recent backup.

Just to clarify what happened: how do you and your wife have your Firefox(es) set up? Do you use separate Firefox profiles under the same Windows user, or separate Windows users?

to be more specific. I have a windows account using a firefox browser and she has a windows account that uses a firefox browser on the same computer. Both firefox accounts share everything.

to be more specific. I have a windows account using a firefox browser and she has a windows account that uses a firefox browser on the same computer. Both firefox accounts share everything.

If users logs into their own Windows Account this can't happen in Windows OS. Separate profile accounts will keep accounts data separate-this is the reason I create a Admin/pswd locked and Family and neither will merge with the other.

The best way I can explain it is:

(1) Firefox stores your data locally in a profile folder. If you never connect the profile to Sync, this data is exclusively local.

Each Windows user usually has a separate profile folder if they sign in under their Windows account because they are stored under

C:\Users\<username>\AppData\Roaming\Mozilla\Firefox\Profiles

(AppData is hidden, so if you want to explore manually, see: https://support.microsoft.com/en-us/windows/view-hidden-files-and-folders-in-windows-97fbc472-c603-9d90-91d0-1166d1d9f4b5)

(2) When you connect a profile in to a Mozilla account, data in that profile is merged with data in the Sync cloud for that Mozilla account.

This allows sharing various categories of data across your different installations. The problem arises when one person's profile is signed into a different person's Mozilla account. Then Sync mixes everything together.