The remote host is missing an update as announced via advisory SSA:2007-200-01.
New mozilla-firefox packages are available for Slackware 11.0 and 12.0 to fix security issues. Note that Firefox 1.5.x has reached its EOL (end of life) and is no longer being updated by mozilla.com. Users of Firefox 1.5.x are encouraged to upgrade to Firefox 2.x. Since we use the official Firefox binaries, these packages should work equally well on earlier Slackware systems. More details about the security issues may be found at this link: http://www.mozilla.org/projects/security/known-vulnerabilities.html#firefox