User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:44.0) Gecko/20100101 Firefox/44.0 Build ID: 20160205155049 Steps to reproduce: In Sync options, there is nothing like an option to delete all history. I think it's quite obvious that this feature is desperately missing from Firefox, for there have always been only workarounds for this. But none has worked for me, I tried to delete all history on one PC, or delete history by months, or to reset Sync password. Nothing worked. Actual results: Still, when I link a new computer to my account, it always loads all synced history, even if it had previously been deleted on a different computer. Expected results: There has to be an evident, transparent way to clear all synced history at all PCs at once, and stop the deleted history to restore on other synced computers. Even if some workaround works, the user has to be given a dedicated, reliable option to delete his browsing data. Also, I see that this issue has been pointed out before, but with little attention, considering how simple and obvious this privacy issue is.
That's very strange - resetting your Firefox Accounts password wipes all the data from the server (which is itself a common cause of complaints!) as the data can no longer be decrypted - and note it must be a "reset password", not "change password". But after doing that, Sync will upload all the current history etc from your local device, which probably includes the data you are trying to avoid syncing. Can you please try to remove all history, then reset (not change) your FxA password and see what happens?
No word from the reporter - please reopen if you have more information.