First of all - don't! :-)
Please ContactUs in case you forgot your certificate password. If you still have access to one or more of your configured notification accounts, we can issue an automatic password notification message. I.e. we can send it to your certificate email address or any other accounts configured on your personal Settings page. If you don't have access to any of those you will probably need a new certificate, but you are welcome to ask before requesting a new certificate.
As usual you should beware of the security implications of us sending the password in clear text. The user scripts tutorial includes instructions for changing the certificate password.