I don't know if you can or not as the last version of Windows I used was Vista. On that and XP a re-install put old files into C:\Windows.old. If Windows 10 does the same it may be possible to salvage your old Profile but it would need somebody more knowledgeable than I to tell you how. For future reference, if your Bookmarks are important to you, make a periodic back-up. Go to Settings > Bookmarks > Manage Bookmarks and then click Import and Backup. That will let you save them as an HTML file which you can then import in the future if needed. A better idea is to sync them to the Mozilla account you must possess to have made your post above. Via that they'd automatically re-appear when you first logged into it from the new installation.