You can install the About Sync extension in Firefox 72 and newer on desktop to check what data is stored on the Sync server via the <b>about:sync</b> page provided by this extension. *About Sync https://addons.mozilla.org/firefox/addon/about-sync/ Close and restart Firefox to access the <b>about:sync</b> page added by this extension (see the about:about page for possible about pages). ---- You can use a USB drive or transfer personal data directly if both profile folders are on the same device. *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile You can copy specific files with Firefox closed from another profile or from a backup to the current profile folder to transfer or recover personal data. *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 (passwords) and key4.db (58+) or key3.db (57 and older) (decryption key) for Passwords saved in the Password Manager<br>if you only have key3.db then make sure to remove an existing key4.db *cert9.db (58+) or cert8.db (57 and older) for (intermediate) certificates stored in the Certificate Manager<br>if you only have cert8.db then make sure to remove an existing cert9.db *persdict.dat for words you added to the spelling 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)