Mozilla Firefox before 2.0.0.6, Thunderbird before 1.5.0.13 and 2.x before 2.0.0.6, and SeaMonkey before 1.1.4 allow remote attackers to execute arbitrary commands via certain vectors associated with launching "a file handling program based on the file extension at the end of the URI," a variant of CVE-2007-4041.  NOTE: the vendor states that "it is still possible to launch a filetype handler based on extension rather than the registered protocol handler."