diff --git a/content/media/mediasource/test/mediasource.js b/content/media/mediasource/test/mediasource.js
index bca2fd2b5286..921adbef9d0a 100644
--- a/content/media/mediasource/test/mediasource.js
+++ b/content/media/mediasource/test/mediasource.js
@@ -1,20 +1,34 @@
 // Helpers for Media Source Extensions tests
 
 function runWithMSE(testFunction) {
-  addLoadEvent(() => SpecialPowers.pushPrefEnv({"set": [[ "media.mediasource.enabled", true ]]}, testFunction));
+  function bootstrapTest() {
+    var ms = new MediaSource();
+
+    var el = document.createElement("video");
+    el.src = URL.createObjectURL(ms);
+    el.preload = "auto";
+
+    document.body.appendChild(el);
+    SimpleTest.registerCleanupFunction(function () {
+      el.parentNode.removeChild(el);
+    });
+
+    testFunction(ms, el);
+  }
+
+  addLoadEvent(function () {
+    SpecialPowers.pushPrefEnv({"set": [[ "media.mediasource.enabled", true ]]},
+                              bootstrapTest);
+  });
 }
 
 function fetchWithXHR(uri, onLoadFunction) {
   var xhr = new XMLHttpRequest();
   xhr.open("GET", uri, true);
-  xhr.responseType = "blob";
-  xhr.addEventListener("load", function (e) {
+  xhr.responseType = "arraybuffer";
+  xhr.addEventListener("load", function () {
     is(xhr.status, 200, "fetchWithXHR load uri='" + uri + "' status=" + xhr.status);
-    var rdr = new FileReader();
-    rdr.addEventListener("load", function (e) {
-      onLoadFunction(e.target.result);
-    });
-    rdr.readAsArrayBuffer(e.target.response);
+    onLoadFunction(xhr.response);
   });
   xhr.send();
 };
diff --git a/content/media/mediasource/test/test_BufferedSeek.html b/content/media/mediasource/test/test_BufferedSeek.html
index bb87efb56773..4f1cd1025cdc 100644
--- a/content/media/mediasource/test/test_BufferedSeek.html
+++ b/content/media/mediasource/test/test_BufferedSeek.html
@@ -12,14 +12,7 @@
 
 SimpleTest.waitForExplicitFinish();
 
-runWithMSE(function () {
-  var ms = new MediaSource();
-
-  var v = document.createElement("video");
-  v.preload = "auto";
-  v.src = URL.createObjectURL(ms);
-  document.body.appendChild(v);
-
+runWithMSE(function (ms, v) {
   ms.addEventListener("sourceopen", function () {
     var sb = ms.addSourceBuffer("video/webm");
 
@@ -51,7 +44,6 @@ runWithMSE(function () {
     v.addEventListener("seeked", function () {
       ok(wasSeeking, "Received expected seeking and seeked events");
       is(v.currentTime, target, "Video currentTime not at target");
-      v.parentNode.removeChild(v);
       SimpleTest.finish();
     });
   });
diff --git a/content/media/mediasource/test/test_FrameSelection.html b/content/media/mediasource/test/test_FrameSelection.html
index d441a044973a..dab987bc3b59 100644
--- a/content/media/mediasource/test/test_FrameSelection.html
+++ b/content/media/mediasource/test/test_FrameSelection.html
@@ -12,14 +12,7 @@
 
 SimpleTest.waitForExplicitFinish();
 
-runWithMSE(function () {
-  var ms = new MediaSource();
-
-  var v = document.createElement("video");
-  v.preload = "auto";
-  v.src = URL.createObjectURL(ms);
-  document.body.appendChild(v);
-
+runWithMSE(function (ms, v) {
   ms.addEventListener("sourceopen", function () {
     var sb = ms.addSourceBuffer("video/webm");
 
@@ -66,7 +59,6 @@ runWithMSE(function () {
       if (target) {
         v.currentTime = target.currentTime;
       } else {
-        v.parentNode.removeChild(v);
         SimpleTest.finish();
       }
     });
diff --git a/content/media/mediasource/test/test_SplitAppend.html b/content/media/mediasource/test/test_SplitAppend.html
index 353ac50fe2e6..34070c456e8b 100644
--- a/content/media/mediasource/test/test_SplitAppend.html
+++ b/content/media/mediasource/test/test_SplitAppend.html
@@ -12,14 +12,7 @@
 
 SimpleTest.waitForExplicitFinish();
 
-runWithMSE(function () {
-  var ms = new MediaSource();
-
-  var v = document.createElement("video");
-  v.preload = "auto";
-  v.src = URL.createObjectURL(ms);
-  document.body.appendChild(v);
-
+runWithMSE(function (ms, v) {
   ms.addEventListener("sourceopen", function () {
     var sb = ms.addSourceBuffer("video/webm");
 
@@ -41,7 +34,6 @@ runWithMSE(function () {
   v.addEventListener("ended", function () {
     is(v.duration, 4, "Video has correct duration");
     is(v.currentTime, 4, "Video has played to end");
-    v.parentNode.removeChild(v);
     SimpleTest.finish();
   });
 });
diff --git a/content/media/mediasource/test/test_SplitAppendDelay.html b/content/media/mediasource/test/test_SplitAppendDelay.html
index 8602ee656e66..9bf26e6dc6be 100644
--- a/content/media/mediasource/test/test_SplitAppendDelay.html
+++ b/content/media/mediasource/test/test_SplitAppendDelay.html
@@ -12,14 +12,7 @@
 
 SimpleTest.waitForExplicitFinish();
 
-runWithMSE(function () {
-  var ms = new MediaSource();
-
-  var v = document.createElement("video");
-  v.preload = "auto";
-  v.src = URL.createObjectURL(ms);
-  document.body.appendChild(v);
-
+runWithMSE(function (ms, v) {
   ms.addEventListener("sourceopen", function () {
     var sb = ms.addSourceBuffer("video/webm");
 
@@ -43,7 +36,6 @@ runWithMSE(function () {
   v.addEventListener("ended", function () {
     is(v.duration, 4, "Video has correct duration");
     is(v.currentTime, 4, "Video has played to end");
-    v.parentNode.removeChild(v);
     SimpleTest.finish();
   });
 });