Bug 1487973 - Disabled dom/media/mediasource/test/test_FrameSelection_mp4.html on windows for frequently faling r=jmaher

Differential Revision: https://phabricator.services.mozilla.com/D21328

--HG--
extra : moz-landing-system : lando

dom/media/mediasource/test/mochitest.ini

@@ -87,7 +87,7 @@ skip-if = android_version == '22' || toolkit == 'android' # bug 1341519, bug 140
 [test_FrameSelection.html]
 skip-if = android_version == '22' || toolkit == 'android' # bug 1341519, bug 1401090
 [test_FrameSelection_mp4.html]
-skip-if = toolkit == 'android' # Not supported on android
+skip-if = toolkit == 'android' || os == 'win' # Not supported on android, # bug 1487973
 [test_HaveMetadataUnbufferedSeek.html]
 skip-if = android_version == '22' || toolkit == 'android' # bug 1342247, bug 1401090
 [test_HaveMetadataUnbufferedSeek_mp4.html]