Firefox behaved slightly differently for already known resources when loading CSS resources involving CSS variables. This could have been used to probe the browser history. This vulnerability affects Thunderbird < 91.9, Firefox ESR < 91.9, and Firefox < 100.

The Performance API did not properly hide the fact whether a request cross-origin resource has observed redirects. This vulnerability affects Firefox < 100.

When reusing existing popups Firefox would have allowed them to cover the fullscreen notification UI, which could have enabled browser spoofing attacks. This vulnerability affects Thunderbird < 91.9, Firefox ESR < 91.9, and Firefox < 100.

Requests initiated through reader mode did not properly omit cookies with a SameSite attribute. This vulnerability affects Thunderbird < 91.9, Firefox ESR < 91.9, and Firefox < 100.

An improper implementation of the new iframe sandbox keyword <code>allow-top-navigation-by-user-activation</code> could lead to script execution without <code>allow-scripts</code> being present. This vulnerability affects Thunderbird < 91.9, Firefox ESR < 91.9, and Firefox < 100.

When closed or sent to the background, Firefox for Android would not properly record and persist HSTS settings.<br>*Note: This issue only affected Firefox for Android. Other operating systems are unaffected.*. This vulnerability affects Firefox < 100.

Documents in deeply-nested cross-origin browsing contexts could have obtained permissions granted to the top-level origin, bypassing the existing prompt and wrongfully inheriting the top-level permissions. This vulnerability affects Thunderbird < 91.9, Firefox ESR < 91.9, and Firefox < 100.

Mozilla developers and community members Nika Layzell, Andrew McCreight, Gabriele Svelto, and the Mozilla Fuzzing Team reported memory safety bugs present in Thunderbird 91.7. 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 Thunderbird < 91.8, Firefox < 99, and Firefox ESR < 91.8.

Mozilla developers and community members Randell Jesup, Sebastian Hengst, and the Mozilla Fuzzing Team reported memory safety bugs present in Firefox 98. 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 < 99.

In unusual circumstances, selecting text could cause text selection caching to behave incorrectly, leading to a crash. This vulnerability affects Firefox < 99.

Due to a layout change, iframe contents could have been rendered outside of its border. This could have led to user confusion or spoofing attacks. This vulnerability affects Thunderbird < 91.8, Firefox < 99, and Firefox ESR < 91.8.

When generating the assembly code for <code>MLoadTypedArrayElementHole</code>, an incorrect AliasSet was used. In conjunction with another vulnerability this could have been used for an out of bounds memory read. This vulnerability affects Thunderbird < 91.8, Firefox < 99, and Firefox ESR < 91.8.

SVG's <code>&lt;use&gt;</code> element could have been used to load unexpected content that could have executed script in certain circumstances. While the specification seems to allow this, other browsers do not, and web developers relied on this property for script security so gecko's implementation was aligned with theirs. This vulnerability affects Firefox < 99.

The sourceMapURL feature in devtools was missing security checks that would have allowed a webpage to attempt to include local files or other files that should have been inaccessible. This vulnerability affects Firefox < 99.

By using a link with <code>rel="localization"</code> a use-after-free could have been triggered by destroying an object during JavaScript execution and then referencing the object through a freed pointer, leading to a potential exploitable crash. This vulnerability affects Thunderbird < 91.8, Firefox < 99, and Firefox ESR < 91.8.

If a compromised content process sent an unexpected number of WebAuthN Extensions in a Register command to the parent process, an out of bounds write would have occurred leading to memory corruption and a potentially exploitable crash. This vulnerability affects Thunderbird < 91.8, Firefox < 99, and Firefox ESR < 91.8.

An unexpected message in the WebGPU IPC framework could lead to a use-after-free and exploitable sandbox escape. We have had reports of attacks in the wild abusing this flaw. This vulnerability affects Firefox < 97.0.2, Firefox ESR < 91.6.1, Firefox for Android < 97.3.0, Thunderbird < 91.6.2, and Focus < 97.3.0.

Removing an XSLT parameter during processing could have lead to an exploitable use-after-free. We have had reports of attacks in the wild abusing this flaw. This vulnerability affects Firefox < 97.0.2, Firefox ESR < 91.6.1, Firefox for Android < 97.3.0, Thunderbird < 91.6.2, and Focus < 97.3.0.

When installing an add-on, Firefox verified the signature before prompting the user; but while the user was confirming the prompt, the underlying add-on file could have been modified and Firefox would not have noticed. This vulnerability affects Firefox < 98, Firefox ESR < 91.7, and Thunderbird < 91.7.

In unusual circumstances, an individual thread may outlive the thread's manager during shutdown. This could have led to a use-after-free causing a potentially exploitable crash. This vulnerability affects Firefox < 98.