Mozilla disabled MD5 in their environment from June 30, 2011 (https://wiki.mozilla.org/CA:MD5and1024). This means that any SSL certificates containing an MD5 signature algorithm will not work in later FireFox browsers after that date.
RapidSSL does not use the MD5 in the certificates we issue. However, it is possible that a small number of older certificates may contain an MD5 signature.
In the next few months RapidSSL will be communicating to any affected customers that they should reissue their certificate.
Reissuing your certificate is a simple process and will ensure your certificate contains a with a SHA-1 signature algorithm.
For instructions on reissuing your certificate please contact support team at ClickSSL.com