USN-4474-2: Firefox regressions

USN-4474-1 fixed vulnerabilities in Firefox. The update introduced various
minor regressions. This update fixes the problem.

We apologize for the inconvenience.

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, trick the user
in to installing a malicious extension, spoof the URL bar, leak sensitive
information between origins, or execute arbitrary code. (CVE-2020-15664,
CVE-2020-15665, CVE-2020-15666, CVE-2020-15670)

It was discovered that NSS incorrectly handled certain signatures.
An attacker could possibly use this issue to expose sensitive information.
(CVE-2020-12400, CVE-2020-12401, CVE-2020-6829)

A data race was discovered when importing certificate information in to
the trust store. An attacker could potentially exploit this to cause an
unspecified impact. (CVE-2020-15668)