Thunderbird before 0.9, when running on Windows systems, uses the default handler when processing javascript: links, which invokes Internet Explorer and may expose the Thunderbird user to vulnerabilities in the version of Internet Explorer that is installed on the user's system. NOTE: since the invocation between multiple products is a common practice, and the vulnerabilities inherent in multi-product interactions are not easily enumerable, this issue might be REJECTED in the future.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A100048
https://exchange.xforce.ibmcloud.com/vulnerabilities/19173
https://bugzilla.mozilla.org/show_bug.cgi?id=263546