The favicon functionality in Firefox before 1.0.3 and Mozilla Suite before 1.7.7 allows remote attackers to execute arbitrary code via a <LINK rel="icon"> tag with a javascript: URL in the href attribute, aka "Firelinking."
The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.