Firefox showing unknown email id from log in field drop down history

An unknown weird email id not even remotely related to me is showing up in the facebook site- email id drop down field.
I have blacked out my email address in the below image.
This is a new Tumbleweed install like only 2 days old, and firefox sync has not even been logged in or synced it yet.
No one other than me has used the machine or has logged in. So how is this happening ?
PS:No i didn’t drunk log in either.