To access https://accounts.firefox.com/ I used my email address xxxx@yahoo.com. I tried to change this email address to my email address xxxx@myonline.be following the prescribed procedure. I then received a message that this email address was already in use. Perhaps I once registered with this email address, but I no longer remember the password. Therefore, I'm unable to create access withe the email address as I'd like. How can I resolve this issue?