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.

What about your other devices? Are the passwords still there?

All the passwords on all my devices are lost. I'm sure no one accessed them as I would have received an email notification. I checked on both Windows and macOS and the passwords in Firefox on both OS are not there anymore. I also checked Firefox on Android and the saved logins are not there either. I don't have a backup as I always relied on Firefox for saved logins. Firefox version is 54.0.1

The bad thing about sync is; Data can be lost if something gets corrupt.

Look on your desktop. Do you see a folder called; Old Firefox?

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

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

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

Thank you for your reply, No I don't have a folder called old Firefox on my desktop. I noticed the problem on my Mac at first. So I started Windows, turned off WiFi and then opened Firefox to check if I can find the saved logins before Firefox syncs and removes them. The problem is that when I opened Firefox (without internet access), all the login details were already gone. The only solution I currently have is to copy the logins one by one from Firefox on my iPhone (which I still have because I disconnected it from the internet). Is there a way to copy the logins from Firefox on iPhone all at once ? Also, do you think Mozilla has a way to restore the passwords (maybe from a backup they might still have on their servers ?)

I don't know. I called for more help.