A use-after-free bug in the usersctp library was reported upstream. We assume this could have led to memory corruption and a potentially exploitable crash.
Mozilla developers and community members Jason Kratzer, Simon Giesecke, Philipp, and Christian Holler reported memory safety bugs present in Firefox 81 and Firefox ESR 78.3. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code.