I'm assuming we are talking about one computer here, as in you reinstalled Windows on one computer, not that you reinstalled Windows on a new computer and are trying to sync bookmarks between the two computers?

If that's the case, Firefox Sync is not intended to be a data backup service, so it doesn't always work well for that purpose.

If you don't have your bookmarks synced on another computer that you still have access to, this it's unlikely that you will be able to recover your data from Firefox Sync.

Hi Mr Branton i just have one computer and i changed the windows version and installed some necessary soft wares same as Firefox. i had a sync account in Firefox.and i remember once i did this and after changing windows version all the logins and bookmarks came back with a sync.but now i try to do this again and it doesnt work.i feel down and don't know what to do.

In that case, unfortunately it's unlikely that you will be able to recover your bookmarks. Firefox Sync is not a backup service.

Sorry.