I have had problems with Firefox Sync for a while. I often reinstall operating systems I use. After each reinstall, I try to sync to my account. I get denied. The email gets returned. I have bypassed this problem a number of times. I am not sure about the exact solution, but either waiting for 24 hours since last attempt to login or fiddling with Firefox Sync settings through my phone which is already logged in seemed to have helped. Fiddling with phone settings does not work anymore. It may have never worked. I have not waited 24 hours since last attempt to login as well, so that could be the fix I am looking for. However, the main problem I have, is that I cannot bypass it in any other way. I am able to login to Firefox Screenshots for example with my account, but I cannot sign in to my Firefox account itself. It is not a good user experience. I understand that this might be used for my own sake, to protect my account from potential intruders...however, I am very dissatisfied with not being able to sign it to my account for over couple of days because of such restrictions. I do not think anyone can do anything about this, it will probably require redesigning existing safety measures just to deal with this obscure problem. I will wait for 24 hours and will update this post after I get the result. Maybe I can help someone else who is on the same boat as I am. I could not see similar problem on the internet other than a few, of which did not portray the problem in a way that I found relatable. But maybe there is another way unbeknownst to me. Either way, thank you for reading. I hope you have a nice day.