The remote host is missing an update to mozilla-firefox announced via advisory DSA 1055-1. Martijn Wargers and Nick Mott described crashes of Mozilla due to the use of a deleted controller context. In theory this could be abused to execute malicious code. Since Mozilla and Firefox share the same codebase, Firefox may be vulnerable as well.
For the stable distribution (sarge) this problem has been fixed in version 1.7.8-1sarge7. For the unstable distribution (sid) this problem has been fixed in version 1.5.dfsg+126.96.36.199-1. We recommend that you upgrade your Mozilla Firefox packages. https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201055-1