Mozilla developers reported memory safety bugs present in Firefox 80 and Firefox ESR 78.2. 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. This vulnerability affects Firefox < 81, Thunderbird < 78.3, and Firefox ESR < 78.3.

When recursing through graphical layers while scrolling, an iterator may have become invalid, resulting in a potential use-after-free. This occurs because the function APZCTreeManager::ComputeClippedCompositionBounds did not follow iterator invalidation rules. This vulnerability affects Firefox < 81, Thunderbird < 78.3, and Firefox ESR < 78.3.

If Firefox is installed to a user-writable directory, the Mozilla Maintenance Service would execute updater.exe from the install location with system privileges. Although the Mozilla Maintenance Service does ensure that updater.exe is signed by Mozilla, the version could have been rolled back to a previous version which would have allowed exploitation of an older bug and arbitrary code execution with System Privileges. *Note: This issue only affected Windows operating systems. Other operating systems are unaffected.*. This vulnerability affects Firefox < 80, Thunderbird < 78.2, Thunderbird < 68.12, Firefox ESR < 68.12, and Firefox ESR < 78.2.

By exploiting an Open Redirect vulnerability on a website, an attacker could have spoofed the site displayed in the download file dialog to show the original site (the one suffering from the open redirect) rather than the site the file was actually downloaded from. This vulnerability affects Firefox < 81, Thunderbird < 78.3, and Firefox ESR < 78.3.

When aborting an operation, such as a fetch, an abort signal may be deleted while alerting the objects to be notified. This results in a use-after-free and we presume that with enough effort it could have been exploited to run arbitrary code. This vulnerability affects Firefox ESR < 68.12 and Thunderbird < 68.12.

The code for downloading files did not properly take care of special characters, which led to an attacker being able to cut off the file ending at an earlier position, leading to a different file type being downloaded than shown in the dialog. This vulnerability affects Firefox ESR < 78.1, Firefox < 79, and Thunderbird < 78.1.

Firefox could be made to load attacker-supplied DLL files from the installation directory. This required an attacker that is already capable of placing files in the installation directory. *Note: This issue only affected Windows operating systems. Other operating systems are unaffected.*. This vulnerability affects Firefox ESR < 78.1, Firefox < 79, and Thunderbird < 78.1.

JIT optimizations involving the Javascript arguments object could confuse later optimizations. This risk was already mitigated by various precautions in the code, resulting in this bug rated at only moderate severity. This vulnerability affects Firefox ESR < 78.1, Firefox < 79, and Thunderbird < 78.1.

When in an endless loop, a website specifying a custom cursor using CSS could make it look like the user is interacting with the user interface, when they are not. This could lead to a perceived broken state, especially when interactions with existing browser dialogs and warnings do not work. This vulnerability affects Firefox ESR < 78.1, Firefox < 79, and Thunderbird < 78.1.

An iframe sandbox element with the allow-popups flag could be bypassed when using noopener links. This could have led to security issues for websites relying on sandbox configurations that allowed popups and hosted arbitrary content. This vulnerability affects Firefox ESR < 78.1, Firefox < 79, and Thunderbird < 78.1.