[USN-3991-3] Firefox regression

USN-3991-1 fixed vulnerabilities in Firefox, and USN-3991-2 fixed a
subsequent regression. The update caused an additional regression that
resulted in Firefox failing to load correctly after executing it in safe
mode. 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, spoof the browser
UI, trick the user in to launching local executable binaries, obtain
sensitive information, conduct cross-site scripting (XSS) attacks, or
execute arbitrary code. (CVE-2019-11691, CVE-2019-11692, CVE-2019-11693,
CVE-2019-11695, CVE-2019-11696, CVE-2019-11699, CVE-2019-11701,
CVE-2019-7317, CVE-2019-9800, CVE-2019-9814, CVE-2019-9817, CVE-2019-9819,
CVE-2019-9820, CVE-2019-9821)

It was discovered that pressing certain key combinations could bypass
addon installation prompt delays. If a user opened a specially crafted
website, an attacker could potentially exploit this to trick them in to
installing a malicious extension. (CVE-2019-11697)

It was discovered that history data could be exposed via drag and drop
of hyperlinks to and from bookmarks. If a user were tricked in to dragging
a specially crafted hyperlink to the bookmark toolbar or sidebar, and
subsequently back in to the web content area, an attacker could
potentially exploit this to obtain sensitive information. (CVE-2019-11698)

A type confusion bug was discovered with object groups and UnboxedObjects.
If a user were tricked in to opening a specially crafted website after
enabling the UnboxedObjects feature, an attacker could potentially
exploit this to bypass security checks. (CVE-2019-9816)