Bug#844688: Firefox - compile with jack audio output support

[trebmuh at tuxfamily.org]

Package: firefox
Version: 45.5.0esr-1

Dear Debian maintainers,

Now that it's supported by upstream, it'd be really great to compile 
Firefox with enabling the jack audio output capability.

See https://bugzilla.mozilla.org/show_bug.cgi?id=783733#c82 for more 
information.

Cheers,
Olivier