You can check if you have the C:\Windows.old folder with your previous personal data. Location used for the main profile that keeps your personal data (Root Directory on about:profiles). *C:\Users\&lt;user&gt;\AppData\Roaming\Mozilla\Firefox\Profiles\&lt;profile&gt; Note that in Windows "AppData" (Mac: ~/Library; Linux: ~/.mozilla) is a hidden folder. ---- You can copy certain files with Firefox closed to the current profile folder to transfer or recover personal data. Note that best is to avoid copying a full profile folder. You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the <b>about:profiles</b> page (Root directory). *Help -> More Troubleshooting Information -> Profile Folder/Directory:<br>Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder *https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data <hr> *bookmarks and history: places.sqlite *favicons: favicons.sqlite *bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder *cookies.sqlite for the Cookies *formhistory.sqlite for saved autocomplete Form Data *logins.json (encrypted logins;32+) and key4.db (decryption key;58+) for Passwords saved in the Password Manager<br>key3.db support ended in 73+; to use key3.db in 58-72, make sure to remove key4.db *cert9.db (58+) for (intermediate) certificates stored in the Certificate Manager *persdict.dat for words added to the spell checker dictionary *permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences) *sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)