Firefox 33 no longer supports keys less than 1024 bits (with good reason). See site compatibility
You can fix this right from Webmin if you use another browser that lets you bypass this type of error. Just login to the Webmin web UI and select: Webmin -> Webmin Configuration -> SSL Encryption -> Self Signed Certificate. Fill in the form (or leave the defaults) and then click the Create Now button. This will update your self-signed certificate for Webmin and you will now be able to access the page from Firefox 33 (With the usual browser warning about an untrusted connection).
Monday, November 03, 2014
certificate - How to bypass the "secure connection failed" warning in Firefox 33 - Super User