firefox regression

USN-3991-1 fixed vulnerabilities in Firefox. The update caused a
regression which resulted in issues when upgrading between Ubuntu
releases. 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)