pkg/51974: HTML5 video playback in firefox freezes

[coypu%sdf.org@localhost]

>Number:         51974
>Category:       pkg
>Synopsis:       HTML5 video playback in firefox freezes
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Feb 16 19:05:00 +0000 2017
>Originator:     coypu
>Release:        pkgsrc-current
>Organization:
>Environment:
NetBSD box 7.99.59 NetBSD 7.99.59 (GENERIC) #1: Tue Feb 14 20:21:35 IST 2017  fly@box:/usr/amd64/sys/arch/amd64/compile/GENERIC amd64

>Description:
Recently (without an update to firefox), video playback will freeze almost always. tested with twitch & youtube. audio works fine.
Did a clean build of pkgsrc-current and used firefox --safe-mode to no avail.
Using PKG_DEFAULT_OPTIONS="-pulse -pulseaudio -alsa oss"
>How-To-Repeat:

>Fix:
I'm investigating, but if anyone else has the same issue, it helps to have confirmation. suspecting audio changes in NetBSD..