Mozilla Firefox — свободный браузер на движке Gecko

When a file download is specified via the `Content-Disposition` header, that directive would be ignored if the file was included via a `<embed>` or `<object>` tag, potentially making a website vulnerable to a cross-site scripting attack. This vulnerability was fixed in Firefox 140, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

Memory safety bugs present in Firefox 139 and Thunderbird 139. 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 was fixed in Firefox 140 and Thunderbird 140.

When a link can be opened in an external application, Firefox for Android will, by default, prompt the user before doing so. An attacker could have bypassed this prompt, potentially exposing the user to security vulnerabilities or privacy leaks in external applications. *This bug only affects Firefox for Android. Other versions of Firefox are unaffected.*. This vulnerability was fixed in Firefox 140.

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. This vulnerability was fixed in Firefox 140, Firefox ESR 115.25, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

When Multi-Account Containers was enabled, DNS requests could have bypassed a SOCKS proxy when the domain name was invalid or the SOCKS proxy was not responding. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

The exception page for the HTTPS-Only feature, displayed when a website is opened via HTTP, lacked an anti-clickjacking delay, potentially allowing an attacker to trick a user into granting an exception and loading a webpage over HTTP. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

A use-after-free in FontFaceSet resulted in a potentially exploitable crash. This vulnerability was fixed in Firefox 140, Firefox ESR 115.25, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

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. This vulnerability was fixed in Firefox 140, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

If a user saved a response from the Network tab in Devtools using the Save As context menu option, that file may not have been saved with the `.download` file extension. This could have led to the user inadvertently running a malicious executable. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

If a user visited a webpage with an invalid TLS certificate, and granted an exception, the webpage was able to provide a WebAuthn challenge that the user would be prompted to complete. This is in violation of the WebAuthN spec which requires "a secure transport established without errors". This vulnerability was fixed in Firefox 140 and Thunderbird 140.