The Mozilla Foundation Security Advisory describes these flaws as:During the plaintext phase of the STARTTLS connection setup, protocol commands could have been injected and evaluated within the encrypted session. When a HTTPS page was embedded in a HTTP page, and there was a service worker registered for the former, the service worker could have intercepted the request for the secure page despite the iframe not being a secure context due to the framing. If a user clicked into a specifically crafted PDF, the PDF reader could be confused into leaking cross-origin information, when said information is served as chunked data. Using the new logical assignment operators in a JavaScript switch statement could have caused a type confusion, leading to a memory corruption and a potentially exploitable crash. Performing garbage collection on re-declared JavaScript variables resulted in a user-after-poison, and a potentially exploitable crash. Mozilla developers reported memory safety bugs present in Firefox 84 and Firefox ESR 78.6. 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