Sorry for your loss of data. Sync wasn't intended a a backup medium (it is intended to synchronize Firefox data between multiple device or Profiles) and the Sync server doesn't keep backups of user data (the "original" data should still be on at least one device connected to that Sync account in the case of failure or loss of one particular device).

Have you disconnected from the Sync server and attempted to restore a backup from within the new Firefox installation? That might get back what you lost as a result of running the 2nd "sync" at least. From my own observations while using Sync, Firefox usually creates or updates the backup file quickly after a "sync process". It does only retains one "backup" for each "day", but it doesn't wait to make the daily backup at a specific time - it seems to be an ongoing process.

Beyond that, unless you have another "backup" of your data, you're SOL with your data.

Problems with bookmarks and history not working properly can be caused by a corrupted places.sqlite database file.

You can check for problems with the places.sqlite database file in the Firefox Profile Folder.

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox
• https://support.mozilla.org/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file

You can try to restore the bookmarks from a recent JSON backup in the bookmarkbackups folder.

• http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox

Hello for the answers and the ideas but as I've figured it myself, I do also understand that this is not a service that can ce recovered after one might uninstall or forget to sync the data between more than one computer. I've read about it and well yes the service doesn't work as a normal back-up system but rather as a system that depends on other syncs with other computers/devices. Thus it's not a system that should be used by a person with just one computer, sync can be replaced by using a normal back-up/sync addon, and there's a few of those to solve this problem.

Even if I lost some bookmarks well I am quite happy that all my passwords have been saved which is 1/2 win-win for me.

Thanks for your help, at least I've understood how to prepare better for the future :P