I am concern about that one can easily see the existing Firefox Account password from Firefox Account > Manage account > Password > Change... > Old password > Show. (This seems to be filled automatically by Firefox) This means that other people can easily check my Firefox account password on my computer if my computer is not logged out. Then the person can sync all the passwords of other websites that are stored in the Firefox server using this Firefox account. Also, one can easily overwrite my current Firefox password without knowing my old password.