Update status for Firefox 42.

tests/html/html.status

 # Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 interactive_test: Skip # Must be run manually.
 dromaeo_smoke_test: Skip # Issue 14521, 8257
 cross_frame_test: Skip # Test reloads itself. Issue 18558
 
 [ $compiler == none && ($runtime == dartium || $runtime == drt) ]
 
@@ skipping 355 matching lines @@
 input_element_test/supported_time: Fail
 input_element_test/supported_week: Fail
 media_stream_test/supported_MediaStreamEvent: Fail
 media_stream_test/supported_MediaStreamTrackEvent: Fail
 mediasource_test/supported: Fail # Behind a flag as of FF 36
 shadow_dom_test/supported: Fail
 speechrecognition_test/supported: Fail
 touchevent_test/supported: Fail
 websql_test/supported: Fail
 
+[ $compiler == dart2js && $runtime == ff && $system == windows ]
+mediasource_test/supported: Pass
+mediasource_test/functional: RuntimeError # Issue 24838
+
 # 'html' tests import the HTML library, so they only make sense in
 # a browser environment.
 [ $runtime == vm ]
 *: Skip
 
 [ $compiler == dart2js && ($runtime == drt || $runtime == ff) ]
 request_animation_frame_test: Skip # Async test hangs.
 
 [ $compiler == dart2js && $csp && ($runtime == drt || $runtime == safari || $runtime == ff || $runtime == chrome || $runtime == chromeOnAndroid) ]
 # Note: these tests are all injecting scripts by design.  This is not allowed under CSP.
@@ skipping 33 matching lines @@
 queryall_test: fail
 track_element_constructor_test: StaticWarning
 transferables_test: StaticWarning
 typed_arrays_range_checks_test: StaticWarning
 typing_test: StaticWarning
 webgl_1_test: StaticWarning
 window_nosuchmethod_test: StaticWarning
 
 [ $compiler == dart2js && $cps_ir ]
 resource_http_test: Crash # (await for(var b in r.openRead()){bytes.addAll(b);}): await for