USN-4165-1 fixed vulnerabilities in Firefox. The update introduced various minor regressions. This update fixes the problems.
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Original advisory details:
Multiple security issues were discovered in Firefox. If a user were tricked in to opening a specially crafted website, an attacker could potentially exploit these to cause a denial of service, bypass security restrictions, bypass same-origin restrictions, conduct cross-site scripting (XSS) attacks, bypass content security policy (CSP) protections, or execute arbitrary code.