Added 3.6 last nite, all bookmarks and history gone th s A.M., how get back

It depends on exactly what you did; or did not do; also on what backups you may have. Firefox tries to automatically keep some auto restore copies of bookmarks and history. If you do an uninstall and reinstall of firefox it will give you the option to retain personal data. If you have previously explicitly made backups of bookmarks etc by exporting them, it should be relatively straightforward to recommence using those files. If that option is not available, what about your ordinary backups , do they include the bookmarks.