Hi rappel, sorry to hear about this problem.

Is this issue on a "desktop" OS (Windows, Mac, Linux) or on your Android device?

Were your saved logins the only data missing or did you notice other changes?

Does Firefox's Password Manager (now called Lockwise in Firefox 70) work to save new logins or does it seem to be nonfunctional? If you need a test site:

https://www.jeffersonscher.com/res/logintest.html

You can check the Password Manager database files (logins.json and key4.db) in the profile folder.

Do you possibly have a logins.json.corrupt file?

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory/Folder:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/Profiles

If you lost personal data then it is possible that a new default-release profile folder has been created. See "Determine if Firefox has created a new profile":

• https://support.mozilla.org/en-US/kb/recover-lost-or-missing-bookmarks

You can open the about:profiles page via the location bar to check whether multiple profiles are present and what profile Firefox currently is using.

• Do NOT click any Remove button on this page.
• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
• https://support.mozilla.org/en-US/kb/dedicated-profiles-firefox-installation