This causes the backout of bug 1184867 even though it has nothing to do with this patch. (it just occurred without that change in http://ftp.mozilla.org/pub/mozilla.org/firefox/tinderbox-builds/fx-team-win64/1438288664/fx-team_win8_64_test-web-platform-tests-3-bm119-tests1-windows-build203.txt.gz) bug 1189138 have slightly changed the timing in which the mediasourcedemuxer is notified of data ; causing the issue to appear.
Created attachment 8641466 [details] [diff] [review] 0001-Bug-1189588-MSE-Remove-MediaSourceDemuxer-NotifyTime.patch
Marking SS based on comment 0 indicating the issue existed prior to the bugs mentioned there.
How severe is this? Does it affect older branches? Do we need to worry about backporting?
the new mediasource is only active in 42. it can be turned on in 41 by switching a pref but I wouldn't worry about it.