During the system reset, did you select to save your data?

Look in your user folder for: Windows.old Your saved data should be here.

unfortunately there's no such folder. I was under the impression that the firefox data gets sync automatically

Sync is meant only to share data. Not as a backup. Too many things can go wrong.

Are you synced to anything? Does it still have its data?

Step 1; Delete the old sync account. Step 2: Create a new sync account using the device that has the data. Step 3: For safety, turn off sync on that device. Step 4: Sync your other device(s). Did it work?

Back up and restore information in Firefox profiles {web link} I use a Legacy add-on that makes backups of my user profile, Just In Case. Unfortunately, it is not compatible with the current Firefox.

Every now and then, open the profile folder and create a copy of the current profile as is to another location on your hard drive. This way you will have a backup.

If you do this each day, you will not lose much data. This should be done with Firefox Closed.

Note: In case you need to restore from these backups, you may need to overwrite old or corrupted files.