This question is no longer an issue, I got information by reading `.mozilla/firefox/[...]/formhistory.sqlite`. Turns out I used a temporary email months ago and Firefox decided to suggest it now. Below is the original question: Hello, Firefox has cached an email I have never seen before. The email domain is paseacuba.com, which is a temporary email service that I never used before. This computer is my own and no one else uses it. I noticed this as a suggestion from a form. (Image below) Could this be explained by any other reason than someone else using this machine ? I was away for the weekend and this happened. Thank you !