firefox regressions

USN-4599-1 and USN-4599-2 fixed vulnerabilities in Firefox. The updates
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, spoof the prompt
for opening an external application, obtain sensitive information, or execute
arbitrary code.