Hi

Windows may have created the C:\Windows.old folder with a backup of your personal data.

Look for the profile folder in the hidden "AppData\Roaming" location.

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>

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.

• 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
  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)

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 Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

ich habe meine Bookmark mit der Endung .json abgespeichert, wie kann ich sie jetzt auf meinen neuen PC installieren

If you created a JSON backup in the Bookmarks Manager (Library) via "Bookmarks -> Show All Bookmarks -> Import & Backup -> Backup" then you can restore this backup via "Bookmarks -> Show All Bookmarks -> Import & Backup -> Restore".

• https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them