The remote host is missing an update as announced via advisory SSA:2008-320-04.

https://secure1.securityspace.com/smysecure/catid.html?in=SSA:2008-320-04

New seamonkey packages are available for Slackware 11.0, 12.0, 12.1, and -current to fix security issues. More details may be found on the Mozilla web site: http://www.mozilla.org/security/known-vulnerabilities/seamonkey11.html