USN-4122-2: Firefox regression

USN-4122-1 fixed vulnerabilities in Firefox. The update caused a
regression that resulted in a crash when changing YouTube playback speed
in some circumstances. 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 obtain sensitive information, bypass Content
Security Policy (CSP) protections, bypass same-origin restrictions,
conduct cross-site scripting (XSS) attacks, cause a denial of service, or
execute arbitrary code. (CVE-2019-5849, CVE-2019-11734, CVE-2019-11735,
CVE-2019-11737, CVE-2019-11738, CVE-2019-11740, CVE-2019-11742,
CVE-2019-11743, CVE-2019-11744, CVE-2019-11746, CVE-2019-11748,
CVE-2019-11749, CVE-2019-11750, CVE-2019-11752)

It was discovered that a compromised content process could log in to a
malicious Firefox Sync account. An attacker could potentially exploit
this, in combination with another vulnerability, to disable the sandbox.
(CVE-2019-9812)

It was discovered that addons.mozilla.org and accounts.firefox.com could
be loaded in to the same content process. An attacker could potentially
exploit this, in combination with another vulnerability that allowed a
cross-site scripting (XSS) attack, to modify browser settings.
(CVE-2019-11741)

It was discovered that the "Forget about this site" feature in the history
pane removes HTTP Strict Transport Security (HSTS) settings for sites on
the pre-load list. An attacker could potentially exploit this to bypass
the protections offered by HSTS. (CVE-2019-11747)