Thank you for your question about the Firefox Sync service.

It appears from your question, that you are using Firefox Sync as a back up service. This is not what Sync is designed to do. The Firefox Sync service takes a copy of the data you wish to include and transfers it to a second device (typically a mobile device such as a tablet or a telephone) running a copy of Firefox. The storage in between all attached devices is both temporary and fragile and is not stable enough to be (and is not designed as) a reliable backup service.

If you have a copy of your Firefox profile for desktop Firefox, you may be able to recover your bookmarks and other data. Please have a read of this article.

If you have a copy of your data on a mobile version of Firefox, please follow these instructions to connect it to Firefox Sync to copy your data.

I understand a bit what you are saying But the thing is before also when I had formatted my computer and after that installing Firefox again and signing in in the sync I got all my bookmarks, history etc without any problem and I had not saved any data But it worked fine but it isn't this time.

Sorry that your data is apparently "lost",

Sync may work as a "backup" for one device, but when the user inadvertently resets the Sync password after the reformat, but before recovering their data from Sync, the data that is wiped from the Sync server - the data is gone, no backup is saved on the Sync server. That data was encrypted and the "key" was generated using the password which was in use the last time the device was connected to the Sync server. The data is useless without the correct "key" which no one ever sees except for the user; it's not set to Mozilla or the Sync server.

There is a warning message for the Reset password process [see the screenshot] that some users don't heed or may not even read. That message is chopped off so as to not reveal my personal Sync account information - it's twice that size in height.

edit for correction of spelling