Were you using Sync? https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer If so, did you have any problems getting signed into Sync after reinstalling Windows and Firefox?

Overall, you should have backed-up your Firefox Profile.

Do you have a C:\Windows.old folder?

You can copy files like these from the C;\Windows.old folder to the current Firefox profile folder to recover specific data.

• bookmarks and history: places.sqlite
• bookmark backups: JSON backups in the bookmarkbackups folder
• cookies.sqlite for the cookies
• formhistory.sqlite for saved form data
• logins.json and key3.db (decryption key) for Passwords saved in the Password Manager
• cert8.db and possibly cert_override.txt for (intermediate) certificates stored in the Certificate Manager
• persdict.dat for words you added to the spelling checker dictionary
• permissions.sqlite for Permissions and possibly content-prefs.sqlite for other Site Preferences
• sessionstore.js for open tabs and pinned tabs

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:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

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

Note that "AppData" (XP: Application Data; Mac: ~/Library; Linux: ~/.mozilla) is a hidden folder.

• http://kb.mozillazine.org/Show_hidden_files_and_folders

My hard drive formatted and i dont have any file or folder from old firefox! I thought that if sign-on to firefox account my data backed up and simply by login to the new OS my saved password and others Returned! Now I What should I do?