A use-after-free vulnerability can occur during WebGL operations. While this results in a potentially exploitable crash, the vulnerability is limited because the memory is freed and reused in a brief window of time during the freeing of the same callstack. This vulnerability affects Firefox < 60.
https://www.mozilla.org/security/advisories/mfsa2018-11/
https://usn.ubuntu.com/3645-1/
https://bugzilla.mozilla.org/show_bug.cgi?id=1444086