Security researchers Tyson Smith and Jesse Schwartzentruber of the BlackBerry Security Automated Analysis Team used the Address Sanitizer tool while fuzzing to discover a mechanism where inserting an ordered list into a document through script could lead to a potentially exploitable crash that can be triggered by web content.
In general these flaws cannot be exploited through email in the Thunderbird and Seamonkey products because scripting is disabled, but are potentially a risk in browser or browser-like contexts.