The Firefox Sync service is the only cloud-based storage feature that is built-in to Firefox. As you discovered, it sometimes seems to sync in the "wrong" direction. I'm not the best person to help with that since I don't use it myself.

You could consider other backup methods, either local or cloud-based, using add-ons or third party software/services.

When you did your Windows restore, did Windows create a folder named C:\Windows.old\? If so, usually your old Firefox data is in there (hidden, but recoverable). We can provide more details if you have that folder.

Yes, I seem to have the C:\Windows.old\ folder. I would appreciate if you could provide more details, I'll have a try.

I love Firefox. I hope in the future the sync function will ask which way we want to sync.

First, if you haven't already, you can switch off the hiding of hidden files and folders. This article has the steps for Windows 7, which I think are similar on Windows 8.1: http://windows.microsoft.com/en-us/windows/show-hidden-files

Next, you can drill down into

C:\Windows.old\Users\your-username\AppData\Roaming\Mozilla\Firefox\Profiles

Here you may find one semi-randomly-named profile folder, or you might find more than one. The most recently modified folder most likely is your previous settings folder.

You could move some key files selectively to your currently live settings folder, or restore the entire old settings folder.

For selective restoration, please see this article: Recover important data from an old profile.

For full restoration steps, please see this thread: https://support.mozilla.org/questions/1024189