--- a/testing/web-platform/meta/media-source/mediasource-append-buffer.html.ini
+++ b/testing/web-platform/meta/media-source/mediasource-append-buffer.html.ini
@@ -5,11 +5,8 @@
     expected: FAIL
 
   [Test appending an empty ArrayBufferView.]
     expected: FAIL
 
   [Test appending an empty ArrayBuffer.]
     expected: FAIL
 
-  [Test SourceBuffer.appendBuffer() triggering an 'ended' to 'open' transition.]
-    disabled:
-      if not debug and (os == "win") and (version == "5.1.2600") and (processor == "x86") and (bits == 32): Unstable

--- a/testing/web-platform/meta/media-source/mediasource-buffered.html.ini
+++ b/testing/web-platform/meta/media-source/mediasource-buffered.html.ini
@@ -1,3 +1,15 @@
 [mediasource-buffered.html]
   type: testharness
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467
+  expected: TIMEOUT
+  [Demuxed content with different lengths]
+    expected: FAIL
+
+  [Muxed tracks with different lengths]
+    expected: FAIL
+
+  [Demuxed content with an empty buffered range on one SourceBuffer]
+    expected: FAIL
+
+  [Muxed content empty buffered ranges.]
+    expected: FAIL
+

deleted file mode 100644
--- a/testing/web-platform/meta/media-source/mediasource-config-change-webm-a-bitrate.html.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[mediasource-config-change-webm-a-bitrate.html]
-  type: testharness
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467

deleted file mode 100644
--- a/testing/web-platform/meta/media-source/mediasource-config-change-webm-av-audio-bitrate.html.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[mediasource-config-change-webm-av-audio-bitrate.html]
-  type: testharness
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467

deleted file mode 100644
--- a/testing/web-platform/meta/media-source/mediasource-config-change-webm-av-video-bitrate.html.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[mediasource-config-change-webm-av-video-bitrate.html]
-  type: testharness
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467

--- a/testing/web-platform/meta/media-source/mediasource-config-change-webm-v-bitrate.html.ini
+++ b/testing/web-platform/meta/media-source/mediasource-config-change-webm-v-bitrate.html.ini
@@ -1,6 +1,5 @@
 [mediasource-config-change-webm-v-bitrate.html]
   type: testharness
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467
   [Tests webm video-only bitrate changes.]
     expected: FAIL
 

--- a/testing/web-platform/meta/media-source/mediasource-duration.html.ini
+++ b/testing/web-platform/meta/media-source/mediasource-duration.html.ini
@@ -1,3 +1,15 @@
 [mediasource-duration.html]
   type: testharness
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467
+  expected: TIMEOUT
+  [Test seek starts on duration truncation below currentTime]
+    expected: TIMEOUT
+
+  [Test appendBuffer completes previous seek to truncated duration]
+    disabled: TIMEOUT or FAIL https://bugzilla.mozilla.org/show_bug.cgi?id=1066467
+
+  [Test endOfStream completes previous seek to truncated duration]
+    expected: TIMEOUT
+
+  [Test setting same duration multiple times does not fire duplicate durationchange]
+    expected: FAIL
+

--- a/testing/web-platform/meta/media-source/mediasource-play-then-seek-back.html.ini
+++ b/testing/web-platform/meta/media-source/mediasource-play-then-seek-back.html.ini
@@ -1,3 +1,6 @@
 [mediasource-play-then-seek-back.html]
   type: testharness
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467
+  expected: TIMEOUT
+  [Test playing then seeking back.]
+    expected: TIMEOUT
+

--- a/testing/web-platform/meta/media-source/mediasource-redundant-seek.html.ini
+++ b/testing/web-platform/meta/media-source/mediasource-redundant-seek.html.ini
@@ -1,3 +1,6 @@
 [mediasource-redundant-seek.html]
   type: testharness
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467
+  expected: TIMEOUT
+  [Test redundant fully prebuffered seek]
+    expected: TIMEOUT
+

--- a/testing/web-platform/meta/media-source/mediasource-seek-beyond-duration.html.ini
+++ b/testing/web-platform/meta/media-source/mediasource-seek-beyond-duration.html.ini
@@ -1,3 +1,9 @@
 [mediasource-seek-beyond-duration.html]
   type: testharness
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467
+  expected: TIMEOUT
+  [Test seeking beyond updated media duration.]
+    expected: TIMEOUT
+
+  [Test seeking beyond media duration.]
+    disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467
+

--- a/testing/web-platform/meta/media-source/mediasource-seek-during-pending-seek.html.ini
+++ b/testing/web-platform/meta/media-source/mediasource-seek-during-pending-seek.html.ini
@@ -1,3 +1,9 @@
 [mediasource-seek-during-pending-seek.html]
   type: testharness
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467
+  expected: TIMEOUT
+  [Test seeking to a new location before transitioning beyond HAVE_METADATA.]
+    expected: TIMEOUT
+
+  [Test seeking to a new location during a pending seek.]
+    expected: TIMEOUT
+

--- a/testing/web-platform/meta/media-source/mediasource-sourcebuffer-mode.html.ini
+++ b/testing/web-platform/meta/media-source/mediasource-sourcebuffer-mode.html.ini
@@ -1,3 +1,6 @@
 [mediasource-sourcebuffer-mode.html]
   type: testharness
-  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1066467
+  expected: TIMEOUT
+  [Test setting SourceBuffer.mode and SourceBuffer.timestampOffset while parsing media segment.]
+    expected: FAIL
+