Mozilla Firefox before 3.0.6 and SeaMonkey do not block links to the (1) about:plugins and (2) about:config URIs from .desktop files, which allows user-assisted remote attackers to bypass the Same Origin Policy and execute arbitrary code with chrome privileges via vectors involving the URL field in a Desktop Entry section of a .desktop file, related to representation of about: URIs as jar:file:// URIs.  NOTE: this issue exists because of an incomplete fix for CVE-2008-4582.