CVE 2006-0884
The WYSIWYG rendering engine ("rich mail" editor) in Mozilla Thunderbird 1.0.7 and earlier allows user-assisted attackers to bypass javascript security settings and obtain sensitive information or cause a crash via an e-mail containing a javascript URI in the SRC attribute of an IFRAME tag, which is executed when the user edits the e-mail.
See the 
CVE page on Mitre.org
for more details.
