When choosing a site-isolated process for a document loaded from a data: URL that was the result of a redirect, Firefox would load that document in the same process as the site that issued the redirect. This bypassed the site-isolation protections against Spectre-like attacks on sites that host an "open redirect". Firefox no longer follows HTTP redirects to data: URLs. This vulnerability affects Firefox < 114.
USN-6143-1 fixed vulnerabilities and USN-6143-2 fixed minor regressions in Firefox. The update introduced several minor regressions. This update fixes the problem. Multiple security issues were discovered in Firefox. If a user were tricked into opening a specially crafted website, an attacker could potentially exploit these to cause a denial of service, obtain sensitive information across domains, or execute arbitrary code. Jun Kokatsu discovered that Firefox did not properly validate site-isolated process for a document loaded from a data: URL that was the result of a redirect, leading to an open redirect attack. An attacker could possibly use this issue to perform phishing attacks.
