Please explain the problem in detail. What happens? What are the exact error message(s) ?

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 <b>about:profiles</b> 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 Firefox 67 and later can use a dedicated profile for each of the Firefox update channels and will lock the profile, so it can only be used by Firefox in a specific installation folder. For Release versions this profile would be a xxxxxxxx.default-release profile, profiles used in older Firefox versions usually used a xxxxxxxx.default profile (a refresh adds a time stamp). *https://support.mozilla.org/en-US/kb/dedicated-profiles-firefox-installation *https://blog.nightly.mozilla.org/2019/01/14/moving-to-a-profile-per-install-architecture/