Google Translated:

Good morning, I have a problem after logging into the browser with syncing Firefox account. On the newly installed windows 10, I downloaded the Firefox browser and logged in to my account for synchronization. All my previous data has disappeared. Can I count on help in recovering my data from my Firefox account? Thank you.

If you didn't back the jason4 files and reinstalled on the same computer wiping everything clean and didn't sync with another device then any data will be gone. So is this the same computer that you reinstalled Windows 10 on?

Thank you for your answer. Unfortunately, I had to upload the system from scratch, because it did not want to start after replacing the processor. I can't access old Firefox folders on my computer. i.e. such browser data is embedded only offline?

Ok, if there was no jason4 backup or folder backup and no Sync of devices - there is no much that can be done here to recover or find the data. So did you backup the system folder offline or there was no backup?

Yes, I have a system backup on the second disk, I will try to restore it, but I don't know if I will be able to restore the previous copy of windows to the new system?

Can I start it in Firefox if I have a .csv file with login data?

Back up and restore information in Firefox profiles https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles