<blockquote> I've lost my password to log into Thunderbird. </blockquote> You don't login into Thunderbird. You do login to your email provider's server via Thunderbird. Hence you cannot change your account password via Thunderbird. You'd have to login to your account via webmail, and change the password on the server. <blockquote> There is no provision to change it, and it wasn't saved by Thunderbird password manager. </blockquote> You can tell Thunderbird to remember your account password. If this is something you didn't do, you'll have to talk to your email provider about password reset options.