A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: A use-after-free in FontFaceSet resulted in a potentially exploitable crash.

A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: An attacker who enumerated resources from the WebCompat extension could have obtained a persistent UUID that identified the browser and persisted between containers and normal/private browsing mode but not profiles.

A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an embed tag. This could have bypassed website security checks that restricted which domains users were allowed to embed.

A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: When a file download is specified via the Content-Disposition header, that directive would be ignored if the file was included via a or tag, potentially making a website vulnerable to a cross-site scripting attack.

A flaw was found in Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: A crafted HTML email using mailbox:/// links can trigger automatic, unsolicited downloads of .pdf files to the user's desktop or home directory without prompting, even if auto-saving is disabled. This behavior can be abused to fill the disk with garbage data (e.g. using /dev/urandom on Linux) or to leak Windows credentials via SMB links when the email is viewed in HTML mode. While user interaction is required to download the .pdf file, visual obfuscation can conceal the download trigger. Viewing the email in HTML mode is enough to load external content.