Firefox has lost all my browsing history and hasn't restored - is there a way to retrieve this?

Firefox stores bookmarks and history in places.sqlite. If you use the Time Machine or other backup then try to restore the places.sqlite file from this backup. *http://www.apple.com/support/timemachine/ Note that restoring places.sqlite gives you the bookmarks as stored in this file, so you lose bookmarks added at a later time. *https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them