Is the information gone (no recovery) or are you not able to access the account?

I am able to access the account only I lost the old data when I tried synchronizing the data. I need to recover from the last synchronized data available. My old website passwords are now not accessible.

Sorry, but the sync servers don't have any history. Only the current data.

Goto each website. At the log-in page, press the 'Forgot Password' link. Such e-mail is always sent to the address on file with the website.

In the event that the passwords information is lost, you should record all information in a separate text file somewhere else on your hard drive, or written down. You can easily copy and paste if you need to do so. If you are concerned about someone else looking at that file, you can compress it using a password.

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.