No backups no recovery possible.

Hi János, I'm guessing that you either were not using Firefox Sync or Sync failed to bring over your bookmarks.

Did you use the type of reset where Windows asks if you want to save your data? In that case, you could look for a new folder named

C:\Windows.old

This temporary folder normally contains a copy of your old Users\<username> folder. For tips on exploring it for Firefox data, see:

https://support.mozilla.org/questions/1448733

Hi,

Unfortunately I do not have a Windows.old folder, because I had to format the whole SSD and repartition it.

Well, I used Sync before and I thought it would work after the reinstallation. But I've read that if you change your Firefox password without account recovery key, all the bookmarks will be lost. Is that true? I didn't remember my Firefox password and I changed it without the account recovery key.

For sync to work the computer you login to sync must have the same data otherwise that data will clear to match the new sync. Sync isn't made for backup only sync between devices and system for the same login when they use another device.

Oh, sorry, it is true that resetting your Mozilla Account password prevents accessing old Sync cloud data. That's because the data was encrypted with your Mozilla Account password before being uploaded to the Sync cloud.

Were there any other devices attached to the same account that still have the old bookmarks?