Mozilla developers and community identified and fixed several memory safety bugs in the browser engine used in Firefox and other Mozilla-based products. Some of these bugs showed evidence of memory corruption under certain circumstances, and we presume that with enough effort at least some of these could be exploited to run arbitrary code.
In general these flaws cannot be exploited through email in the Thunderbird product because scripting is disabled, but are potentially a risk in browser or browser-like contexts.
Bob Clary, Christian Holler, Nils Ohlmeier, Gary Kwong, Jesse Ruderman, Carsten Book, and Randell Jesup reported memory safety problems and crashes that affect Firefox ESR 38.5 and Firefox 43.
Bob Clary, Carsten Book, Christian Holler, Nicolas Pierron, Eric Rescorla, Tyson Smith, Gabor Krizsanits, and Randell Jesup reported memory safety problems and crashes that affect Firefox 43.