Firefox is a free and open-source web browser developed by the Mozilla Foundation. A use-after-free vulnerability can occur after deleting a selection element due to a weak reference to the select element in the options collection, which gets garbage collected, and results in a potentially exploitable crash. Originally, it was discovered by Nils.

A use-after-free vulnerability can occur after deleting a selection element due to a weak reference to the select element in the options collection. This results in a potentially exploitable crash. This vulnerability affects Thunderbird < 60.4, Firefox ESR < 60.4, and Firefox < 64.