[nemeth88]

If your browser has the password saved then you can extract it now and save it to a more secure place, like a password manager. Presumably you could then use it to update your Yahoo! account email to a current, working address.

As noted here - http://stackoverflow.com/questions/30013032/prevent-user-to-... you can get it using your browser's web inspector dev tool.

[claudius]

FWIW, Firefox lets you view the stored passwords directly (about:preferences#security → Saved Logins → Show Passwords). Very useful feature :)

[Nition]

If it's Chrome, you can just go to Settings -> Show advanced settings... -> Manage passwords. Then click on a password and click Show.