Disaster step by step: 1. Run old Firefox 28, using a separate profile named "Firefox 28", and log in to my old sync account (the one used on Firefox 28). In the old sync account i have saved tons of useful bookmarks and data. Got a device name "Admin's Firefox on HP-Laptop". 2. Check all my old bookmarks and they are fine. Stupid of me i didn't make a backup at that point. 3. Run new Firefox 34.0.5, using a separate profile named "default", and log in to my new sync account (the one used on Firefox 29 and on). In the new sync account i have saved a few bookmarks only. Got a device name "Admin's Firefox on HP-Laptop" again. Stupid of me i didn't pick another name. Didn't imagine what was about to happen. 4. What happened: All of my precious data which was stored on the old sync account got replaced by the few bookmarks of the new sync account. And by replaced i mean replaced ON THE SYNC SERVER. Now the old sync server has the very little data of the new sync account and i have lost all my precious data!!! That little bug of Firefox cost me all of my data on the server. People, please help me find a solution to recover my data that was stored on the old sync server and got replaced. I have no backup of the lost bookmarks nor backup of a profile that contains them. P.S.: I used the default setting to sync, which was to merge data. P.S.2: I don't maintain a personal old Firefox Sync server. Who is the administrator of the old sync server maintained by Mozilla? Does he keep image backup? Maybe he could extract my data from an image backup. A pre-today date would be fine!