pkg/51969: Change firefox package defaults

[coypu%sdf.org@localhost]

>Number:         51969
>Category:       pkg
>Synopsis:       Change firefox package defaults
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Feb 14 15:55:00 +0000 2017
>Originator:     coypu
>Release:        pkgsrc-current
>Organization:
>Environment:
NetBSD box 7.99.59 NetBSD 7.99.59 (GENERIC) #0: Mon Feb 13 21:47:38 IST 2017  fly@box:/home/fly/maxv2/sys/arch/amd64/compile/GENERIC amd64

>Description:
- Enabling widevine by default poses a security risk, see:
  https://bugzilla.mozilla.org/show_bug.cgi?id=1295853

- Using non-standard audio options (alsa, pulseaudio), audio doesn't work as-is, and requires setup. With no explanation for how to set it up (e.g. MESSAGE) people just assume it doesn't work.

Worse still, until martin's commit, using the default ALSA on firefox for playing audio would crash immediately.
>How-To-Repeat:

>Fix: