Redirect Firefox output to /dev/null by default

Because the Firefox output is never used by default, /dev/null is the
perfect place for it.

Fixes Issue #7677

Signed-off-by: Luke Inman-Semerau <luke.semerau@gmail.com>
Fix NullPointerException when File#listFiles() returns null

See issue 1934 where the NPE is listed in a few comments. The problem is
that File#listFiles() can return null, see documentation:

http://docs.oracle.com/javase/7/docs/api/java/io/File.html#listFiles%28%29

This fixes all the listFiles call sites that aren't part of an assertion
in a test case.
Compiling and adding as a third-party dep the shaded Jetty 5 used by RC.

We really shouldn't be editing the code, and there's no good reason for us to treat
the antiquated version of Jetty used by RC as anything other than a third-party
dependency.
Updating Windows native events libraries for supported Firefox ESR releases
Non-functional change to Visual C project file for Firefox previous ESR native events lib
Remove unused import subprocess.PIPE