Try using this add-on. https://addons.mozilla.org/en-us/firefox/addon/xmarks-sync/

I doubt if your data disappeared from the Sync server, but it may take a while for all your Sync data to make it back into what amounts to a clean installation. Sync wasn't really intended as a backup medium, it works best at synchronizing existing data in bursts of data as that data is added and for adding data on a device that hasn't been connected for a short time.

That said, Mozilla is working on a new generation of Sync which hopefully is more user friendly in many ways.

i don't know, but luckily enough that i didn't loose too many bookmarks. But this brings a great questions... can Mozilla take a look at the data in terms of kb that the back up severs get? If the new data is significantly smaller than the old one, there would be a change of corrupt data (i assume that was what happened to me) so something like this could be prevented?

You should always backup your personal data locally yourself or at least on a web servers that is meant for backing up (cloud) to make sure that you won't lose it in case of problems.

See also:

• http://kb.mozillazine.org/Profile_backup
• https://support.mozilla.org/kb/Backing+up+your+information

Well, regards everything. Can my data be recovered from the sever somehow? Or it is completely vanished?

Firefox won't vanish your data automatically....

Try with new SYNC.

I tried to uninstall Firefox 22 right after that to retry Firefox 21 with new sync, but it didn't work.

Didn't work mean?

Got connected with firefox sync?

No data's in Firefox Sync server?

I mean it got the same result. Missing Bookmarks, missing Theme, not what i originally have.