Sorry about that happening to you. ''Been there, done that; learned from that.'' Data should be "restored" from another device that is connected to that Firefox Account that still has your Firefox data. If you were using a solitary device with Sync, you weren't using Sync as intended; which is to synchronize data between multiple devices, not as a "backup media" for one device when reinstalling Windows. Do you have a '''C:\Windows.old ''' folder? <br> See this support posting: https://support.mozilla.org/en-US/questions/1293283#answer-1329034 Also, you did get a '''warning message''' when you '''''reset''''' your Firefox Account password that explained that all your data would be deleted from the Sync server and your data would be gone. The original password held your "key" to your encrypted data when that data was away from "your control" on your Firefox installations. ''IMO, overly strong encryption for all Firefox data other than login data that the user has saved in Firefox; considering the number of questions threads like this that we see here. But that is my opinion brought about by users not reading that warning message, and their haste to be done with an arduous process of reinstalling Windows, with Firefox typically being the last step to getting back online. But it is the way it is since Firefox 29 Australis with regards to Mozilla Firefox Sync security for user data that is stored for Firefox users. And surely better that what existed with Firefox 4.0 thru Firefox 28.0 with the Sync 1.5 version of security. This Sync 2.0 version is far better and more straightforward, IMO. But hey, I am not an IT professional, just a computer user since 1984 and have been retired for 10 years, giving me the time to help out here with Firefox support; been a Firefox user since 2002 and just "paying it forward" for all the help I received in the mid-00's when I was first 'learning the ropes'.