First be sure of what you are talking about. Are you saying the passwords were not saved during an update, or are you having problems when you try to sync?

I'm using 25th version of firefox, now I wanna update it to last version. in 25th version my passwords saved and these are sync successful! but after do update to last version, I lose my passwords! thank you :|

i said when I do update firefox; my passwords doesnt sync!

said *

I'm using 25th version of firefox, now I wanna update it to last version. in 25th version my passwords saved and these are sync successful! but after do update to last version, I lose my passwords! thank you :|

Somewhere around Firefox 29, Firefox changed how Sync accounts work. Please see this article for more information: Sync your Firefox bookmarks, history, passwords and more. If you can't do that in Firefox 33, you may want to install Firefox 29 temporarily to do the account change, and then update to Firefox 33. This article has information on how to find clean old versions of Firefox: Install an older version of Firefox.

If you mean sync in a more informal sense, of having your data correctly converted correctly to a newer version on your computer (not involving the Firefox Sync service), then there would be a different method for that.