I was using a Firefox account linked to an E-mail on my PC and iPhone (both of them are running latest version of Firefox). Recently I replaced my PC by a new one, and I tried to sign in to Firefox by this same account on my new PC (latest version of Firefox too). But Firefox told me to set a new password, so I did it, sign in with new password and tried to sync, and nothing was synced. I tried the device management in my account page, but I can't see anything on my new PC except itself, meanwhile I can see my old PC and iPhone itself on my iOS Firefox. I tried to re-sign in on my iPhone, and shockingly found that I can only use my old password to successfully sign in, the new password working on my new PC is a wrong one for my phone. Then I tried to delete the account with new password on PC. After delete successful, sign in on my PC with that E-mail was correctly reported as "unknown account", but I can still sign in with the exact same E-mail and the old password on my phone, like nothing happened at all. At the same time, even if I tried the exact same combination of E-mail and old password on PC, the result is always "unknown account", like it already be deleted.