http://www.mozillazine.org/talkback.html?article=4960
ZitatBranches have been created for three of mozilla.org's latest releases, in order to fix an external windows protocol handler bug. The fix involves disabling the shell: protocol handler, which was found to enable pages to run executables on Windows via a link. Builds should officially be available shortly, and there will also be an XPI offered to disable the pref. Alternatively, you can set the pref "network.protocol-handler.external.shell" in about:config to 'false' to also remove the exploit.
More information about the exploit can be found in this post on the Full Disclosure mailing list.
UPDATE! The XPI to disable the pref is now available.