The Firefox Sync service is <u>not a backup service</u>, so it may not work for that purpose. While it's true that some people are able to recover bookmarks from Firefox Sync, those cases are rare and very much come down to luck. If you are logged into a secondary computer, you can [[Export Firefox bookmarks to an HTML file to back up or transfer bookmarks|export your bookmarks to an HTML file]] and then [[Import Bookmarks from an HTML file|import that file on your computer you just reset]]. However, if this is your only device that was connected to Firefox Sync, it's unlikely that you will be able to recover the bookmarks from Firefox Sync.