No bug - Re-disable test_mixed_principals.html on all platforms.

content/media/test/mochitest.ini

@@ -378,7 +378,7 @@ skip-if = buildapp == 'b2g' || toolkit == 'android' # mimetype check, bug 969289
 [test_mediarecorder_unsupported_src.html]
 [test_metadata.html]
 [test_mixed_principals.html]
-skip-if = (os == 'linux'  && debug) || (toolkit == 'android' && debug) || toolkit == 'gonk' # bug 567954 and intermittent leaks
+skip-if = true # bug 567954 and intermittent leaks
 [test_mozHasAudio.html]
 [test_networkState.html]
 [test_new_audio.html]