diff --git a/dom/archivereader/test/helpers.js b/dom/archivereader/test/helpers.js
index 3ba430436049..f6ad40a9c1fe 100644
--- a/dom/archivereader/test/helpers.js
+++ b/dom/archivereader/test/helpers.js
@@ -3,8 +3,6 @@
  * http://creativecommons.org/publicdomain/zero/1.0/
  */
 
-var testGenerator;
-
 function runTest()
 {
   SimpleTest.waitForExplicitFinish();
@@ -12,8 +10,7 @@ function runTest()
   SpecialPowers.pushPrefEnv({'set': [ ["dom.archivereader.enabled", true] ]}, function() {
     SpecialPowers.createFiles(filesToCreate(),
                               function (files) {
-                                testGenerator = testSteps(files);
-                                return testGenerator.next();
+                                testSteps(files);
                               },
                               function (msg) {
                                 ok(false, "File creation error: " + msg);
@@ -25,7 +22,6 @@ function runTest()
 function finishTest()
 {
   SpecialPowers.popPrefEnv(function() {
-    testGenerator.close();
     SimpleTest.finish();
   });
 }
diff --git a/dom/archivereader/test/test_basic.html b/dom/archivereader/test/test_basic.html
index b3e5ab852ace..516c9d8e4547 100644
--- a/dom/archivereader/test/test_basic.html
+++ b/dom/archivereader/test/test_basic.html
@@ -212,7 +212,6 @@
       ok(false, "ArchiveReader.getFiles() should not return an 'error'");
       markTestDone();
     }
-    yield undefined;
   }
 
   </script>
diff --git a/dom/archivereader/test/test_nonUnicode.html b/dom/archivereader/test/test_nonUnicode.html
index 6237ce10f9fe..f24e400ec601 100644
--- a/dom/archivereader/test/test_nonUnicode.html
+++ b/dom/archivereader/test/test_nonUnicode.html
@@ -51,7 +51,6 @@
   function testSteps(files)
   {
     test1(files[0]);
-    yield undefined;
   }
 
 
diff --git a/dom/archivereader/test/test_zip_in_zip.html b/dom/archivereader/test/test_zip_in_zip.html
index 7e381a1efeae..69e1c1de78c8 100644
--- a/dom/archivereader/test/test_zip_in_zip.html
+++ b/dom/archivereader/test/test_zip_in_zip.html
@@ -25,8 +25,6 @@
 
     // The input is 4 nested zip archives:
     doLoop(binaryFile, 4);
-
-    yield undefined;
   }
 
   function doLoop(blob, loop)
diff --git a/dom/base/test/browser_use_counters.js b/dom/base/test/browser_use_counters.js
index e4d29654be1e..27ca44161356 100644
--- a/dom/base/test/browser_use_counters.js
+++ b/dom/base/test/browser_use_counters.js
@@ -83,7 +83,7 @@ add_task(function* () {
   let Telemetry = Cc["@mozilla.org/base/telemetry;1"].getService(Ci.nsITelemetry);
   Telemetry.canRecordExtended = gOldParentCanRecord;
 
-  yield ContentTask.spawn(gBrowser.selectedBrowser, { oldCanRecord: gOldContentCanRecord }, function (arg) {
+  yield ContentTask.spawn(gBrowser.selectedBrowser, { oldCanRecord: gOldContentCanRecord }, function* (arg) {
     Cu.import("resource://gre/modules/PromiseUtils.jsm");
     yield new Promise(resolve => {
       let telemetry = Cc["@mozilla.org/base/telemetry;1"].getService(Ci.nsITelemetry);
@@ -127,7 +127,7 @@ function grabHistogramsFromContent(use_counter_middlefix, page_before = null) {
   }).then(gather, gather);
 }
 
-var check_use_counter_iframe = Task.async(function* (file, use_counter_middlefix, check_documents=true) {
+var check_use_counter_iframe = async function(file, use_counter_middlefix, check_documents=true) {
   info("checking " + file + " with histogram " + use_counter_middlefix);
 
   let newTab = gBrowser.addTab( "about:blank");
@@ -138,13 +138,13 @@ var check_use_counter_iframe = Task.async(function* (file, use_counter_middlefix
   // interested in.
   let [histogram_page_before, histogram_document_before,
        histogram_docs_before, histogram_toplevel_docs_before] =
-      yield grabHistogramsFromContent(use_counter_middlefix);
+      await grabHistogramsFromContent(use_counter_middlefix);
 
   gBrowser.selectedBrowser.loadURI(gHttpTestRoot + "file_use_counter_outer.html");
-  yield waitForPageLoad(gBrowser.selectedBrowser);
+  await waitForPageLoad(gBrowser.selectedBrowser);
 
   // Inject our desired file into the iframe of the newly-loaded page.
-  yield ContentTask.spawn(gBrowser.selectedBrowser, { file: file }, function(opts) {
+  await ContentTask.spawn(gBrowser.selectedBrowser, { file: file }, function(opts) {
     Cu.import("resource://gre/modules/PromiseUtils.jsm");
     let deferred = PromiseUtils.defer();
 
@@ -174,12 +174,12 @@ var check_use_counter_iframe = Task.async(function* (file, use_counter_middlefix
   // The histograms only get recorded when the document actually gets
   // destroyed, which might not have happened yet due to GC/CC effects, etc.
   // Try to force document destruction.
-  yield waitForDestroyedDocuments();
+  await waitForDestroyedDocuments();
 
   // Grab histograms again and compare.
   let [histogram_page_after, histogram_document_after,
        histogram_docs_after, histogram_toplevel_docs_after] =
-      yield grabHistogramsFromContent(use_counter_middlefix, histogram_page_before);
+      await grabHistogramsFromContent(use_counter_middlefix, histogram_page_before);
 
   is(histogram_page_after, histogram_page_before + 1,
      "page counts for " + use_counter_middlefix + " after are correct");
@@ -189,9 +189,9 @@ var check_use_counter_iframe = Task.async(function* (file, use_counter_middlefix
     is(histogram_document_after, histogram_document_before + 1,
        "document counts for " + use_counter_middlefix + " after are correct");
   }
-});
+};
 
-var check_use_counter_img = Task.async(function* (file, use_counter_middlefix) {
+var check_use_counter_img = async function(file, use_counter_middlefix) {
   info("checking " + file + " as image with histogram " + use_counter_middlefix);
 
   let newTab = gBrowser.addTab("about:blank");
@@ -202,13 +202,13 @@ var check_use_counter_img = Task.async(function* (file, use_counter_middlefix) {
   // interested in.
   let [histogram_page_before, histogram_document_before,
        histogram_docs_before, histogram_toplevel_docs_before] =
-      yield grabHistogramsFromContent(use_counter_middlefix);
+      await grabHistogramsFromContent(use_counter_middlefix);
 
   gBrowser.selectedBrowser.loadURI(gHttpTestRoot + "file_use_counter_outer.html");
-  yield waitForPageLoad(gBrowser.selectedBrowser);
+  await waitForPageLoad(gBrowser.selectedBrowser);
 
   // Inject our desired file into the img of the newly-loaded page.
-  yield ContentTask.spawn(gBrowser.selectedBrowser, { file: file }, function(opts) {
+  await ContentTask.spawn(gBrowser.selectedBrowser, { file: file }, function*(opts) {
     Cu.import("resource://gre/modules/PromiseUtils.jsm");
     let deferred = PromiseUtils.defer();
 
@@ -239,12 +239,12 @@ var check_use_counter_img = Task.async(function* (file, use_counter_middlefix) {
   // The histograms only get recorded when the document actually gets
   // destroyed, which might not have happened yet due to GC/CC effects, etc.
   // Try to force document destruction.
-  yield waitForDestroyedDocuments();
+  await waitForDestroyedDocuments();
 
   // Grab histograms again and compare.
   let [histogram_page_after, histogram_document_after,
        histogram_docs_after, histogram_toplevel_docs_after] =
-      yield grabHistogramsFromContent(use_counter_middlefix, histogram_page_before);
+      await grabHistogramsFromContent(use_counter_middlefix, histogram_page_before);
   is(histogram_page_after, histogram_page_before + 1,
      "page counts for " + use_counter_middlefix + " after are correct");
   is(histogram_document_after, histogram_document_before + 1,
@@ -255,9 +255,9 @@ var check_use_counter_img = Task.async(function* (file, use_counter_middlefix) {
   // one for the SVG image itself.
   ok(histogram_docs_after >= histogram_docs_before + 2,
      "document counts are correct");
-});
+};
 
-var check_use_counter_direct = Task.async(function* (file, use_counter_middlefix, xfail=false) {
+var check_use_counter_direct = async function(file, use_counter_middlefix, xfail=false) {
   info("checking " + file + " with histogram " + use_counter_middlefix);
 
   let newTab = gBrowser.addTab( "about:blank");
@@ -268,10 +268,10 @@ var check_use_counter_direct = Task.async(function* (file, use_counter_middlefix
   // interested in.
   let [histogram_page_before, histogram_document_before,
        histogram_docs_before, histogram_toplevel_docs_before] =
-      yield grabHistogramsFromContent(use_counter_middlefix);
+      await grabHistogramsFromContent(use_counter_middlefix);
 
   gBrowser.selectedBrowser.loadURI(gHttpTestRoot + file);
-  yield ContentTask.spawn(gBrowser.selectedBrowser, null, function*() {
+  await ContentTask.spawn(gBrowser.selectedBrowser, null, function*() {
     Cu.import("resource://gre/modules/PromiseUtils.jsm");
     yield new Promise(resolve => {
       let listener = () => {
@@ -292,12 +292,12 @@ var check_use_counter_direct = Task.async(function* (file, use_counter_middlefix
   // The histograms only get recorded when the document actually gets
   // destroyed, which might not have happened yet due to GC/CC effects, etc.
   // Try to force document destruction.
-  yield waitForDestroyedDocuments();
+  await waitForDestroyedDocuments();
 
   // Grab histograms again and compare.
   let [histogram_page_after, histogram_document_after,
        histogram_docs_after, histogram_toplevel_docs_after] =
-      yield grabHistogramsFromContent(use_counter_middlefix, histogram_page_before);
+      await grabHistogramsFromContent(use_counter_middlefix, histogram_page_before);
   (xfail ? todo_is : is)(histogram_page_after, histogram_page_before + 1,
                          "page counts for " + use_counter_middlefix + " after are correct");
   (xfail ? todo_is : is)(histogram_document_after, histogram_document_before + 1,
@@ -306,4 +306,4 @@ var check_use_counter_direct = Task.async(function* (file, use_counter_middlefix
      "top level document counts are correct");
   ok(histogram_docs_after >= histogram_docs_before + 1,
      "document counts are correct");
-});
+};
diff --git a/dom/base/test/referrer_helper.js b/dom/base/test/referrer_helper.js
index c46bdea7a49c..5615b038ddba 100644
--- a/dom/base/test/referrer_helper.js
+++ b/dom/base/test/referrer_helper.js
@@ -66,7 +66,7 @@ function resetState() {
 /**
  * testing if anchor and area referrer attributes are honoured (1174913)
  */
-var tests = (function() {
+var tests = (function*() {
 
   // enable referrer attribute
   yield SpecialPowers.pushPrefEnv({"set": [['network.http.enablePerElementReferrer', true]]}, advance);
@@ -97,6 +97,6 @@ var tests = (function() {
     };
   };
 
-  // complete.  Be sure to yield so we don't call this twice.
-  yield SimpleTest.finish();
-})();
\ No newline at end of file
+  // complete.
+  SimpleTest.finish();
+})();
diff --git a/dom/base/test/test_audioNotificationSilent_audioFile.html b/dom/base/test/test_audioNotificationSilent_audioFile.html
index 0b3b89580101..38f7221499cb 100644
--- a/dom/base/test/test_audioNotificationSilent_audioFile.html
+++ b/dom/base/test/test_audioNotificationSilent_audioFile.html
@@ -28,11 +28,7 @@ var observer = {
 };
 
 function continueTest() {
-  try {
-    generator.next();
-  } catch (e if e instanceof StopIteration) {
-    error("Stop test because of exception!");
-  }
+  generator.next();
 }
 
 function audioPlayingStart() {
@@ -58,16 +54,16 @@ function finish() {
   SimpleTest.finish();
 }
 
-function runTest() {
+function* runTest() {
   yield audioPlayingStart();
 
   yield audioBecomeSilentDuringPlaying();
 
-  yield finish();
+  finish();
 }
 
 continueTest();
 
 </script>
 </body>
-</html>
\ No newline at end of file
+</html>
diff --git a/dom/base/test/test_audioNotificationSilent_webAudio.html b/dom/base/test/test_audioNotificationSilent_webAudio.html
index de4165f8e438..ef180952c00b 100644
--- a/dom/base/test/test_audioNotificationSilent_webAudio.html
+++ b/dom/base/test/test_audioNotificationSilent_webAudio.html
@@ -30,11 +30,7 @@ var observer = {
 };
 
 function continueTest() {
-  try {
-    generator.next();
-  } catch (e if e instanceof StopIteration) {
-    error("Stop test because of exception!");
-  }
+  generator.next();
 }
 
 function playOscillatorNode() {
@@ -86,18 +82,18 @@ function startAudioContext() {
   }
 }
 
-function runTest() {
+function* runTest() {
   yield startAudioContext();
 
   yield audioPlayingStart();
 
   yield audioBecomeSilentDuringPlaying();
 
-  yield finish();
+  finish();
 }
 
 continueTest();
 
 </script>
 </body>
-</html>
\ No newline at end of file
+</html>
diff --git a/dom/base/test/test_bug1163743.html b/dom/base/test/test_bug1163743.html
index 69d1c8c33f54..e718bca29626 100644
--- a/dom/base/test/test_bug1163743.html
+++ b/dom/base/test/test_bug1163743.html
@@ -20,7 +20,7 @@ var advance = function() { tests.next(); };
 /**
  * testing legacy support for origin-when-crossorigin (1163743)
  */
-var tests = (function() {
+var tests = (function*() {
   var iframe = document.getElementById("testframe");
   const sjs = "/tests/dom/base/test/bug704320.sjs?action=generate-policy-test";
 
@@ -29,8 +29,8 @@ var tests = (function() {
   yield iframe.src = sjs + "&policy=" + escape(' origin-when-crossorigin');
   yield checkIndividualResults("origin-when-cross-origin", ["origin", "full"]);
 
-  // complete.  Be sure to yield so we don't call this twice.
-  yield SimpleTest.finish();
+  // complete.
+  SimpleTest.finish();
 })();
 
 </script>
diff --git a/dom/base/test/test_bug1165501.html b/dom/base/test/test_bug1165501.html
index fe932d4ea87c..35bee854fd3c 100644
--- a/dom/base/test/test_bug1165501.html
+++ b/dom/base/test/test_bug1165501.html
@@ -21,7 +21,7 @@ var advance = function() { tests.next(); };
  * testing if policy is overwritten if there are two meta statements (1165501)
  * XXX: would be nice to test this with CSP and meta as well
  */
-var tests = (function() {
+var tests = (function*() {
   var iframe = document.getElementById("testframe");
   const sjs = "/tests/dom/base/test/bug704320.sjs?action=generate-policy-test";
 
@@ -36,8 +36,8 @@ var tests = (function() {
   yield checkIndividualResults("no-referrer then default", ["full"]);
 
 
-  // complete.  Be sure to yield so we don't call this twice.
-  yield SimpleTest.finish();
+  // complete.
+  SimpleTest.finish();
 })();
 
 </script>
diff --git a/dom/base/test/test_bug544642.html b/dom/base/test/test_bug544642.html
index 350360f41c5b..a0ee76b8ac57 100644
--- a/dom/base/test/test_bug544642.html
+++ b/dom/base/test/test_bug544642.html
@@ -17,10 +17,10 @@ var gen = runTest();
 
 addLoadEvent(function() { gen.next(); });
 
-function runTest() {
+function* runTest() {
   var iframe = $('iframe');
-  iframe.onerror = function() { gen.send("error"); };
-  iframe.onload = function() { gen.send("load"); };
+  iframe.onerror = function() { gen.next("error"); };
+  iframe.onload = function() { gen.next("load"); };
 
   iframe.src = "data:text/plain,hello";
   is((yield), "load", "plaintext data");
@@ -34,8 +34,6 @@ function runTest() {
   //is((yield), "error", "invalid http");
 
   SimpleTest.finish();
-  
-  yield undefined;
 }
 
 </script>
diff --git a/dom/base/test/test_bug590870.html b/dom/base/test/test_bug590870.html
index 0faa2f4b6080..980ba7bbaf55 100644
--- a/dom/base/test/test_bug590870.html
+++ b/dom/base/test/test_bug590870.html
@@ -15,11 +15,11 @@
 <script class="testbody" type="application/javascript;version=1.8">
 
 SimpleTest.waitForExplicitFinish();
-window.addEventListener("message", function(e) { gen.send(e.data) }, false);
+window.addEventListener("message", function(e) { gen.next(e.data) }, false);
 
 var gen = runTest();
 
-function runTest() {
+function* runTest() {
   var iframe = $('iframe');
   iframe.src = "http://noxul.example.com/tests/dom/base/test/file_bug590870.html";
   is((yield), true, "shouldn't be able to create XUL elements");
@@ -28,7 +28,6 @@ function runTest() {
   is((yield), false, "should be able to create XUL elements");
 
   SimpleTest.finish();
-  yield undefined;
 }
 
 </script>
diff --git a/dom/base/test/test_bug682592.html b/dom/base/test/test_bug682592.html
index c2dc8ed3a484..a9b66442d771 100644
--- a/dom/base/test/test_bug682592.html
+++ b/dom/base/test/test_bug682592.html
@@ -51,14 +51,14 @@ var testFrame = document.getElementById("iframe-test");
 
 refFrame.addEventListener("load", function() {
   testFrame.addEventListener("load", function() {
-    try {
-      tests.next();
+    let {done} = tests.next();
+    if (!done) {
       ok(compareSnapshots(snapshotWindow(testFrame.contentWindow), 
                           snapshotWindow(refFrame.contentWindow), true)[0], 
          "bidi is not detected correctly");
 
       testFrame.contentWindow.location.reload();
-    } catch (err if err instanceof StopIteration) {
+    } else {
       SimpleTest.finish();
     }
   }, false);
@@ -78,7 +78,7 @@ function strMult(aStr, aNumber) {
   return strMult(aStr, aNumber - 1) + aStr;
 }
 
-function runTests () {
+function* runTests () {
   var ltr = "", prefix = null;
   var refContainer = refFrame.contentDocument.getElementById('content');
   var testContainer, textNode;
diff --git a/dom/base/test/test_bug704320.html b/dom/base/test/test_bug704320.html
index 5c8e46c03d37..a536807fb88c 100644
--- a/dom/base/test/test_bug704320.html
+++ b/dom/base/test/test_bug704320.html
@@ -41,7 +41,7 @@ var advance = function() { tests.next(); };
  * This is the main test routine -- serialized by use of a generator.
  * It performs all tests in sequence using in the same iframe.
  */
-var tests = (function() {
+var tests = (function*() {
   SimpleTest.requestLongerTimeout(4);
   var iframe = document.getElementById("testframe");
   iframe.onload = function() {
@@ -57,8 +57,8 @@ var tests = (function() {
     yield checkExpectedGlobalResults();
   }
 
-  // complete.  Be sure to yield so we don't call this twice.
-  yield SimpleTest.finish();
+  // complete.
+  SimpleTest.finish();
 })();
 
 </script>
diff --git a/dom/base/test/test_bug704320_policyset.html b/dom/base/test/test_bug704320_policyset.html
index 8188a9480652..ac4eafa7e66b 100644
--- a/dom/base/test/test_bug704320_policyset.html
+++ b/dom/base/test/test_bug704320_policyset.html
@@ -22,7 +22,7 @@ var advance = function() { tests.next(); };
  * It resets the counter, then performs two tests in sequence using
  * the same iframe.
  */
-var tests = (function() {
+var tests = (function*() {
   var iframe = document.getElementById("testframe");
   const sjs = "/tests/dom/base/test/bug704320.sjs?action=generate-policy-test";
 
@@ -89,8 +89,8 @@ var tests = (function() {
   yield iframe.src = sjs + "&policy=" + escape('\f OrigIn');
   yield checkIndividualResults("origin case insensitive", ["origin"]);
 
-  // complete.  Be sure to yield so we don't call this twice.
-  yield SimpleTest.finish();
+  // complete.
+  SimpleTest.finish();
 })();
 
 </script>
diff --git a/dom/base/test/test_bug704320_policyset2.html b/dom/base/test/test_bug704320_policyset2.html
index b9cc74e3d782..9bb5b3d27c90 100644
--- a/dom/base/test/test_bug704320_policyset2.html
+++ b/dom/base/test/test_bug704320_policyset2.html
@@ -22,7 +22,7 @@ var advance = function() { tests.next(); };
  * It resets the counter, then performs two tests in sequence using
  * the same iframe.
  */
-var tests = (function() {
+var tests = (function*() {
   var iframe = document.getElementById("testframe");
   const sjs = "/tests/dom/base/test/bug704320.sjs?action=generate-policy-test";
 
@@ -30,8 +30,8 @@ var tests = (function() {
   yield iframe.src = sjs + "&policy=" + escape(' \f\r\n\t  ');
   yield checkIndividualResults("whitespace only policy", ["full"]);
 
-  // complete.  Be sure to yield so we don't call this twice.
-  yield SimpleTest.finish();
+  // complete.
+  SimpleTest.finish();
 })();
 
 </script>
diff --git a/dom/base/test/test_bug704320_preload.html b/dom/base/test/test_bug704320_preload.html
index d7f2fc72d39b..bba534ca45b5 100644
--- a/dom/base/test/test_bug704320_preload.html
+++ b/dom/base/test/test_bug704320_preload.html
@@ -22,7 +22,7 @@ var advance = function() { tests.next(); };
  * It resets the counter, then performs two tests in sequence using
  * the same iframe.
  */
-var tests = (function() {
+var tests = (function*() {
   var iframe = document.getElementById("testframe");
 
   // reset the counter
@@ -47,8 +47,8 @@ var tests = (function() {
   // check the second test
   yield checkResults(finalizePreloadReuse);
 
-  // complete.  Be sure to yield so we don't call this twice.
-  yield SimpleTest.finish();
+  // complete.
+  SimpleTest.finish();
 })();
 
 // Helper functions below.
diff --git a/dom/base/test/test_change_policy.html b/dom/base/test/test_change_policy.html
index 76816f01feed..4ab5b9ce38eb 100644
--- a/dom/base/test/test_change_policy.html
+++ b/dom/base/test/test_change_policy.html
@@ -78,7 +78,7 @@ function resetState() {
  * It resets the counter, then performs two tests in sequence using
  * the same iframe.
  */
-var tests = (function() {
+var tests = (function*() {
   var iframe = document.getElementById("testframe");
   var sjs = "/tests/dom/base/test/referrer_change_server.sjs?action=generate-policy-test";
 
@@ -114,8 +114,8 @@ var tests = (function() {
   yield iframe.src = sjs + "&policy=" + escape('unsafe-url') + "&name=" + name + "&newPolicy=" + escape('no-referrer');
   yield checkIndividualResults("no-referrer (changed) with unsafe-url first", ["none"], [name+'no-referrer']);
 
-  // complete.  Be sure to yield so we don't call this twice.
-  yield SimpleTest.finish();
+  // complete.
+  SimpleTest.finish();
 })();
 
 </script>
diff --git a/dom/base/test/test_img_referrer.html b/dom/base/test/test_img_referrer.html
index 16259bcc3930..2f7bffc4fae7 100644
--- a/dom/base/test/test_img_referrer.html
+++ b/dom/base/test/test_img_referrer.html
@@ -82,7 +82,7 @@ function resetState() {
 /**
  * testing if img referrer attribute is honoured (1165501)
  */
-var tests = (function() {
+var tests = (function*() {
 
   // enable referrer attribute
   yield SpecialPowers.pushPrefEnv({"set": [['network.http.enablePerElementReferrer', true]]}, advance);
@@ -174,8 +174,8 @@ var tests = (function() {
   yield iframe.src = sjs + "&imgPolicy=" + escape('default') + "&policy=" + escape('unsafe-url') + "&name=" + name;
   yield checkIndividualResults("unsafe-url in meta, default in img", ["full"], [name]);
 
-  // complete.  Be sure to yield so we don't call this twice.
-  yield SimpleTest.finish();
+  // complete.
+  SimpleTest.finish();
 })();
 
 </script>
diff --git a/dom/browser-element/mochitest/browserElement_ActiveStateChange.js b/dom/browser-element/mochitest/browserElement_ActiveStateChange.js
index cfbc1cb1e185..60fb09d321fe 100644
--- a/dom/browser-element/mochitest/browserElement_ActiveStateChange.js
+++ b/dom/browser-element/mochitest/browserElement_ActiveStateChange.js
@@ -4,7 +4,6 @@ SimpleTest.waitForExplicitFinish();
 browserElementTestHelpers.setEnabledPref(true);
 
 var fileURL = 'chrome://mochitests/content/chrome/dom/browser-element/mochitest/file_browserElement_ActiveStateChange.html';
-var generator = runTests();
 var testFrame;
 var ac;
 
@@ -17,55 +16,46 @@ function error(aMessage) {
   finish();
 }
 
-function continueTest() {
-  try {
-    generator.next();
-  } catch (e if e instanceof StopIteration) {
-    error("Stop test because of exception!");
-  }
-}
-
 function finish() {
   document.body.removeChild(testFrame);
   SimpleTest.finish();
 }
 
 function setCommand(aArg) {
-  assert(!!ac, "Audio channel doesn't exist!");
-  info("# Command = " + aArg);
+  return new Promise(resolve => {
+    assert(!!ac, "Audio channel doesn't exist!");
+    info("# Command = " + aArg);
 
-  testFrame.src = fileURL + '#' + aArg;
-  var expectedActive = false;
-  switch (aArg) {
-    case 'play':
-      expectedActive = true;
-      break;
-    case 'pause':
-      expectedActive = false;
-      break;
-    default :
-      error("Undefined command!");
-  }
-
-  ac.onactivestatechanged = () => {
-    ac.onactivestatechanged = null;
-    ac.isActive().onsuccess = (e) => {
-      is(expectedActive, e.target.result,
-         "Correct active state = " + expectedActive);
-      continueTest();
+    testFrame.src = fileURL + '#' + aArg;
+    var expectedActive = false;
+    switch (aArg) {
+      case 'play':
+        expectedActive = true;
+        break;
+      case 'pause':
+        expectedActive = false;
+        break;
+      default :
+        error("Undefined command!");
     }
-  };
+
+    ac.onactivestatechanged = () => {
+      ac.onactivestatechanged = null;
+      ac.isActive().onsuccess = (e) => {
+        is(expectedActive, e.target.result,
+           "Correct active state = " + expectedActive);
+        resolve();
+      };
+    };
+  });
 }
 
-function runTests() {
-  setCommand('play');
-  yield undefined;
+async function runTests() {
+  await setCommand('play');
 
-  setCommand('pause');
-  yield undefined;
+  await setCommand('pause');
 
   finish();
-  yield undefined;
 }
 
 function setupTestFrame() {
@@ -74,7 +64,6 @@ function setupTestFrame() {
   testFrame.src = fileURL;
 
   function loadend() {
-    testFrame.removeEventListener('mozbrowserloadend', loadend);
     ok("allowedAudioChannels" in testFrame, "allowedAudioChannels exist");
     var channels = testFrame.allowedAudioChannels;
     is(channels.length, 9, "9 audio channel by default");
@@ -85,7 +74,7 @@ function setupTestFrame() {
     ok("isActive" in ac, "isActive exists");
     ok("onactivestatechanged" in ac, "onactivestatechanged exists");
 
-    generator.next();
+    runTests();
   }
 
   function alertError(e) {
@@ -94,7 +83,7 @@ function setupTestFrame() {
     error(message);
   }
 
-  testFrame.addEventListener('mozbrowserloadend', loadend);
+  testFrame.addEventListener('mozbrowserloadend', loadend, {once: true});
   testFrame.addEventListener('mozbrowsershowmodalprompt', alertError);
   document.body.appendChild(testFrame);
 }
diff --git a/dom/browser-element/mochitest/browserElement_AudioChannelSeeking.js b/dom/browser-element/mochitest/browserElement_AudioChannelSeeking.js
index f354a9d82e68..796d17d41cc3 100644
--- a/dom/browser-element/mochitest/browserElement_AudioChannelSeeking.js
+++ b/dom/browser-element/mochitest/browserElement_AudioChannelSeeking.js
@@ -32,11 +32,7 @@ function error(aMessage) {
 }
 
 function continueTest() {
-  try {
-    generator.next();
-  } catch (e if e instanceof StopIteration) {
-    error("Stop test because of exception!");
-  }
+  generator.next();
 }
 
 function finish() {
@@ -74,7 +70,7 @@ function setCommand(aArg) {
   }
 }
 
-function runTests() {
+function* runTests() {
   setCommand('play');
   yield undefined;
 
@@ -91,7 +87,6 @@ function runTests() {
   yield undefined;
 
   finish();
-  yield undefined;
 }
 
 function setupTestFrame() {
diff --git a/dom/browser-element/mochitest/browserElement_NoAudioTrack.js b/dom/browser-element/mochitest/browserElement_NoAudioTrack.js
index 47f0fd5244d4..32fcfb6e95ff 100644
--- a/dom/browser-element/mochitest/browserElement_NoAudioTrack.js
+++ b/dom/browser-element/mochitest/browserElement_NoAudioTrack.js
@@ -25,11 +25,7 @@ function error(aMessage) {
 }
 
 function continueTest() {
-  try {
-    generator.next();
-  } catch (e if e instanceof StopIteration) {
-    error("Stop test because of exception!");
-  }
+  generator.next();
 }
 
 function finish() {
@@ -45,7 +41,7 @@ function setCommand(aArg) {
   testFrame.src = fileURL + '#' + aArg;
 }
 
-function runTests() {
+function* runTests() {
   setCommand('play');
   yield undefined;
 
@@ -54,7 +50,6 @@ function runTests() {
   yield undefined;
 
   finish();
-  yield undefined;
 }
 
 function setupTestFrame() {
diff --git a/dom/devicestorage/test/test_app_permissions.html b/dom/devicestorage/test/test_app_permissions.html
index 528d3e9832ae..aaa834388f70 100644
--- a/dom/devicestorage/test/test_app_permissions.html
+++ b/dom/devicestorage/test/test_app_permissions.html
@@ -432,7 +432,7 @@ function testComplete(iframe, data) {
   }
 }
 
-function runTest() {
+function* runTest() {
   while (gData.length > 0) {
     var iframe = document.createElement('iframe');
     var data = gData.pop();
diff --git a/dom/devicestorage/test/test_fs_app_permissions.html b/dom/devicestorage/test/test_fs_app_permissions.html
index ac4db92b6b79..32ccf5382d98 100644
--- a/dom/devicestorage/test/test_fs_app_permissions.html
+++ b/dom/devicestorage/test/test_fs_app_permissions.html
@@ -550,7 +550,7 @@ function testComplete(iframe, data) {
   }
 }
 
-function runTest() {
+function* runTest() {
   while (gData.length > 0) {
     let iframe = document.createElement('iframe');
     let data = gData.shift();
diff --git a/dom/events/test/bug426082.html b/dom/events/test/bug426082.html
index 8eaaa7391a44..90c95575978e 100644
--- a/dom/events/test/bug426082.html
+++ b/dom/events/test/bug426082.html
@@ -61,19 +61,20 @@ var gNeedsPaint = false;
 function executeTests() {
   var testYielder = tests();
   function execNext() {
-    try {
-      if (!gNeedsPaint) {
-        testYielder.next();
-        button.getBoundingClientRect(); // Flush.
-        gNeedsPaint = true;
+    if (!gNeedsPaint) {
+      let {done} = testYielder.next();
+      if (done) {
+        return;
       }
-      SimpleTest.executeSoon(execNext);
-    } catch (e) {}
+      button.getBoundingClientRect(); // Flush.
+      gNeedsPaint = true;
+    }
+    SimpleTest.executeSoon(execNext);
   }
   execNext();
 }
 
-function tests() {
+function* tests() {
   window.addEventListener("MozAfterPaint", paintListener, false);
   normalButtonCanvas = takeSnapshot();
   // Press the button.
diff --git a/dom/events/test/bug656379-1.html b/dom/events/test/bug656379-1.html
index d7a04e3bfbf6..a6e94e5b67b4 100644
--- a/dom/events/test/bug656379-1.html
+++ b/dom/events/test/bug656379-1.html
@@ -77,19 +77,20 @@ var gNeedsPaint = false;
 function executeTests() {
   var testYielder = tests();
   function execNext() {
-    try {
-      if (!gNeedsPaint) {
-        testYielder.next();
-        button.getBoundingClientRect(); // Flush.
-        gNeedsPaint = true;
+    if (!gNeedsPaint) {
+      let {done} = testYielder.next();
+      if (done) {
+        return;
       }
-      SimpleTest.executeSoon(execNext);
-    } catch (e) {}
+      button.getBoundingClientRect(); // Flush.
+      gNeedsPaint = true;
+    }
+    SimpleTest.executeSoon(execNext);
   }
   execNext();
 }
 
-function tests() {
+function* tests() {
   window.addEventListener("MozAfterPaint", paintListener, false);
   normalButtonCanvas = takeSnapshot();
   // Press the button.
diff --git a/dom/events/test/test_bug415498.xul b/dom/events/test/test_bug415498.xul
index 009431cb1400..70d19828654d 100644
--- a/dom/events/test/test_bug415498.xul
+++ b/dom/events/test/test_bug415498.xul
@@ -52,12 +52,8 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=415498
     }
 
     function nextTest() {
-      try {
-        gTestsIterator.next();
-      } catch (err) {
-          ok(err instanceof StopIteration,
-             "Some other exception was thrown than what we expected!");
-
+      let {done} = gTestsIterator.next();
+      if (done) {
         if (gConsole && gConsoleListener) {
           gConsole.unregisterListener(gConsoleListener);
         }
@@ -65,7 +61,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=415498
       }
     }
 
-    function testsIterator() {
+    function* testsIterator() {
 
       var browser = $("browser");
       browser.addEventListener("load", function() {
diff --git a/dom/events/test/test_bug656379-2.html b/dom/events/test/test_bug656379-2.html
index d53abce41e6f..40e62fc66434 100644
--- a/dom/events/test/test_bug656379-2.html
+++ b/dom/events/test/test_bug656379-2.html
@@ -30,7 +30,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=656379
 
 /** Test for Bug 656379 **/
 SimpleTest.waitForExplicitFinish();
-function tests() {
+function* tests() {
   synthesizeMouseAtCenter($("label1"), { type: "mousemove" });
   yield undefined;
   is($("button1").matches(":hover"), true,
@@ -67,10 +67,11 @@ function tests() {
 function executeTests() {
   var testYielder = tests();
   function execNext() {
-    try {
-      testYielder.next();
-      SimpleTest.executeSoon(execNext);
-    } catch(e) {}
+    let {done} = testYielder.next();
+    if (done) {
+      return;
+    }
+    SimpleTest.executeSoon(execNext);
   }
   execNext();
 }
diff --git a/dom/file/tests/test_mozfiledataurl.html b/dom/file/tests/test_mozfiledataurl.html
index b842336d8de0..9596550de1d7 100644
--- a/dom/file/tests/test_mozfiledataurl.html
+++ b/dom/file/tests/test_mozfiledataurl.html
@@ -10,8 +10,8 @@
 <p id="display">
 <iframe id=inner></iframe>
 <iframe id=iframe></iframe>
-<img id=img onload="gen.send(event);">
-<audio id=audio onloadeddata="gen.send(event);">
+<img id=img onload="gen.next(event);">
+<audio id=audio onloadeddata="gen.next(event);">
 </p>
 <div id="content" style="display: none">
 
@@ -24,7 +24,7 @@ try {
 } catch(e) { }
 
 window.addEventListener("message", function(e) {
-  gen.send(JSON.parse(e.data));
+  gen.next(JSON.parse(e.data));
 }, false);
 
 const innerSameSiteURI = "file_mozfiledataurl_inner.html";
@@ -59,12 +59,12 @@ function start() {
 
 SimpleTest.waitForExplicitFinish();
 
-function runTest([imgFile, audioFile, docFile, xhrFile]) {
+function* runTest([imgFile, audioFile, docFile, xhrFile]) {
   inner = document.getElementById('inner');
   img = document.getElementById('img');
   audio = document.getElementById('audio');
   iframe = document.getElementById('iframe');
-  inner.onload = function() { gen.send("inner loaded"); };
+  inner.onload = function() { gen.next("inner loaded"); };
 
   // Attempt to load a image in this document
   var fileurl = URL.createObjectURL(imgFile);
@@ -194,7 +194,7 @@ function runTest([imgFile, audioFile, docFile, xhrFile]) {
   // Attempt to load file url using XHR
   fileurl = URL.createObjectURL(xhrFile);
   xhr = new XMLHttpRequest;
-  xhr.onload = function() { gen.send("XHR finished"); };
+  xhr.onload = function() { gen.next("XHR finished"); };
   xhr.open("GET", fileurl);
   xhr.send();
   is((yield), "XHR finished", "correct gen.next()");
@@ -216,8 +216,6 @@ function runTest([imgFile, audioFile, docFile, xhrFile]) {
   is(res.didError, true, "load failed successfully");
 
   SimpleTest.finish();
-
-  yield undefined;
 }
 </script>
 </pre>
diff --git a/dom/html/test/forms/test_input_color_input_change_events.html b/dom/html/test/forms/test_input_color_input_change_events.html
index d9e7558f8f36..6e7055c424a3 100644
--- a/dom/html/test/forms/test_input_color_input_change_events.html
+++ b/dom/html/test/forms/test_input_color_input_change_events.html
@@ -25,7 +25,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=885996
     test.next();
   });
 
-  function runTest() {
+  function* runTest() {
     MockColorPicker.init(window);
     var element = null;
 
@@ -100,7 +100,6 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=885996
 
     MockColorPicker.cleanup();
     SimpleTest.finish();
-    yield undefined;
   }
 
   </script>
diff --git a/dom/html/test/forms/test_input_color_picker_initial.html b/dom/html/test/forms/test_input_color_picker_initial.html
index 4b6a45cbb7ad..cfbff14065f7 100644
--- a/dom/html/test/forms/test_input_color_picker_initial.html
+++ b/dom/html/test/forms/test_input_color_picker_initial.html
@@ -24,7 +24,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=885996
     test.next();
   });
 
-  function runTest() {
+  function* runTest() {
     MockColorPicker.init(window);
     var element = null;
 
@@ -47,7 +47,6 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=885996
 
     MockColorPicker.cleanup();
     SimpleTest.finish();
-    yield undefined;
   }
 
   </script>
diff --git a/dom/html/test/forms/test_input_color_picker_popup.html b/dom/html/test/forms/test_input_color_picker_popup.html
index 239f140145ae..c7952bb02473 100644
--- a/dom/html/test/forms/test_input_color_picker_popup.html
+++ b/dom/html/test/forms/test_input_color_picker_popup.html
@@ -45,7 +45,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=885996
     test.next();
   });
 
-  function runTest() {
+  function* runTest() {
     MockColorPicker.init(window);
     var element = null;
 
@@ -112,7 +112,6 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=885996
 
     MockColorPicker.cleanup();
     SimpleTest.finish();
-    yield undefined;
   }
 
   </script>
diff --git a/dom/html/test/forms/test_input_color_picker_update.html b/dom/html/test/forms/test_input_color_picker_update.html
index c40791323091..ae12d485a6c1 100644
--- a/dom/html/test/forms/test_input_color_picker_update.html
+++ b/dom/html/test/forms/test_input_color_picker_update.html
@@ -26,7 +26,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=885996
     test.next();
   });
 
-  function runTest() {
+  function* runTest() {
     MockColorPicker.init(window);
     var element = null;
 
@@ -68,7 +68,6 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=885996
 
     MockColorPicker.cleanup();
     SimpleTest.finish();
-    yield undefined;
   }
 
   </script>
diff --git a/dom/html/test/forms/test_input_textarea_set_value_no_scroll.html b/dom/html/test/forms/test_input_textarea_set_value_no_scroll.html
index 829daa8c97b5..c5e04bcbcbda 100644
--- a/dom/html/test/forms/test_input_textarea_set_value_no_scroll.html
+++ b/dom/html/test/forms/test_input_textarea_set_value_no_scroll.html
@@ -89,7 +89,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=829606
     }, 0);
   }
 
-  function runTest()
+  function* runTest()
   {
     test('input');
     yield undefined;
@@ -98,7 +98,6 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=829606
     testCorrectUpdateOnScroll();
     yield undefined;
     SimpleTest.finish();
-    yield undefined;
   }
 
   gTestRunner = runTest();
diff --git a/dom/html/test/forms/test_input_typing_sanitization.html b/dom/html/test/forms/test_input_typing_sanitization.html
index 0896f19df884..fa7376c98b22 100644
--- a/dom/html/test/forms/test_input_typing_sanitization.html
+++ b/dom/html/test/forms/test_input_typing_sanitization.html
@@ -49,14 +49,9 @@ function urlify(aStr) {
 
 function runTestsForNextInputType()
 {
-  try {
-    testRunner.next();
-  } catch (e) {
-    if (e.toString() == '[object StopIteration]') {
-      SimpleTest.finish();
-    } else {
-      throw StopIteration;
-    }
+  let {done} = testRunner.next();
+  if (done) {
+    SimpleTest.finish();
   }
 }
 
@@ -116,7 +111,7 @@ var submitMethod = submitForm;
 
 SimpleTest.waitForExplicitFinish();
 
-function runTest()
+function* runTest()
 {
   SimpleTest.requestLongerTimeout(4);
 
diff --git a/dom/html/test/test_anchor_ping.html b/dom/html/test/test_anchor_ping.html
index 4a39bcefee7c..9809429e9fcd 100644
--- a/dom/html/test/test_anchor_ping.html
+++ b/dom/html/test/test_anchor_ping.html
@@ -23,11 +23,11 @@ Cu.import("resource://gre/modules/Promise.jsm");
 Cu.import("resource://gre/modules/Task.jsm");
 
 addLoadEvent(function () {
-  Task.spawn(function run_tests() {
+  Task.spawn(function* run_tests() {
     while (tests.length) {
       let test = tests.shift();
       info("-- running " + test.name);
-      yield Task.spawn(test);
+      yield* test();
     }
 
     SimpleTest.finish();
diff --git a/dom/html/test/test_bug209275.xhtml b/dom/html/test/test_bug209275.xhtml
index f74e5e5fb390..76dd352054d1 100644
--- a/dom/html/test/test_bug209275.xhtml
+++ b/dom/html/test/test_bug209275.xhtml
@@ -100,7 +100,7 @@ function continueTest() {
 var iframe = document.getElementById("iframe");
 var iframeCw = iframe.contentWindow;
 
-function run() {
+function* run() {
   var iframe = document.getElementById("iframe");
   var iframeCw = iframe.contentWindow;
 
@@ -245,7 +245,6 @@ function run() {
      "Wrong href after document.open().");
 
   SimpleTest.finish();
-  yield undefined;
 }
 
 window.addEventListener("load", function() {
diff --git a/dom/html/test/test_bug481335.xhtml b/dom/html/test/test_bug481335.xhtml
index f8a51df69ccd..7303f72f87aa 100644
--- a/dom/html/test/test_bug481335.xhtml
+++ b/dom/html/test/test_bug481335.xhtml
@@ -62,7 +62,7 @@ function checkLinkColor(aElmId, aExpectedColor, aMessage) {
   return true;
 }
 
-function testIterator() {
+function* testIterator() {
   // After first load
   $("newparent").appendChild($("t"));
   is($("t").href, "http://www.example.com/" + rand,
@@ -106,7 +106,6 @@ function testIterator() {
     yield undefined;
   }
   SimpleTest.finish();
-  yield undefined;
 }
 
 addLoadEvent(function() {
diff --git a/dom/html/test/test_formSubmission.html b/dom/html/test/test_formSubmission.html
index 0edfeaeb8547..aeaabc3cff92 100644
--- a/dom/html/test/test_formSubmission.html
+++ b/dom/html/test/test_formSubmission.html
@@ -686,7 +686,7 @@ function onFilesSet() {
   });
 }
 
-function runTest() {
+function* runTest() {
   // Set up the expectedSub array
   fileReader1 = new FileReader;
   fileReader1.readAsBinaryString(myFile1);
@@ -816,7 +816,6 @@ function runTest() {
                     expectedSub.concat(expectedAugment), "send augmented FormData");
 
   SimpleTest.finish();
-  yield undefined;
 }
 
 </script>
diff --git a/dom/html/test/test_formSubmission2.html b/dom/html/test/test_formSubmission2.html
index 2d0eb42f9724..4c337fef8d26 100644
--- a/dom/html/test/test_formSubmission2.html
+++ b/dom/html/test/test_formSubmission2.html
@@ -162,7 +162,7 @@ function clickImage(aTarget, aX, aY)
   aTarget.style.left = "";
 }
 
-function runTest() {
+function* runTest() {
   // Make normal submission
   var form = $("form");
   var iframe = $("target_iframe");
@@ -212,7 +212,6 @@ function runTest() {
   }
 
   SimpleTest.finish();
-  yield undefined;
 }
 
 </script>
diff --git a/dom/indexedDB/test/browserHelpers.js b/dom/indexedDB/test/browserHelpers.js
index c61c78943490..22f43fd18d63 100644
--- a/dom/indexedDB/test/browserHelpers.js
+++ b/dom/indexedDB/test/browserHelpers.js
@@ -16,7 +16,7 @@ function runTest()
 function finishTestNow()
 {
   if (testGenerator) {
-    testGenerator.close();
+    testGenerator.return();
     testGenerator = undefined;
   }
 }
@@ -40,7 +40,7 @@ function finishTest()
 
 function grabEventAndContinueHandler(event)
 {
-  testGenerator.send(event);
+  testGenerator.next(event);
 }
 
 function errorHandler(event)
diff --git a/dom/indexedDB/test/browser_forgetThisSiteAdd.html b/dom/indexedDB/test/browser_forgetThisSiteAdd.html
index 2982012a6c62..734a20954681 100644
--- a/dom/indexedDB/test/browser_forgetThisSiteAdd.html
+++ b/dom/indexedDB/test/browser_forgetThisSiteAdd.html
@@ -7,7 +7,7 @@
     <title>Indexed Database Test</title>
 
     <script type="text/javascript;version=1.7">
-      function testSteps()
+      function* testSteps()
       {
         let request = indexedDB.open("browser_forgetThisSite.js", 11);
         request.onerror = grabEventAndContinueHandler;
diff --git a/dom/indexedDB/test/browser_forgetThisSiteGet.html b/dom/indexedDB/test/browser_forgetThisSiteGet.html
index 948eaa68f133..835f3771f7a2 100644
--- a/dom/indexedDB/test/browser_forgetThisSiteGet.html
+++ b/dom/indexedDB/test/browser_forgetThisSiteGet.html
@@ -7,7 +7,7 @@
     <title>Indexed Database Test</title>
 
     <script type="text/javascript;version=1.7">
-      function testSteps()
+      function* testSteps()
       {
         let request = indexedDB.open("browser_forgetThisSite.js");
         request.onerror = grabEventAndContinueHandler;
diff --git a/dom/indexedDB/test/browser_permissionsPrompt.html b/dom/indexedDB/test/browser_permissionsPrompt.html
index 0ee698b97bf2..17f5817d6df7 100644
--- a/dom/indexedDB/test/browser_permissionsPrompt.html
+++ b/dom/indexedDB/test/browser_permissionsPrompt.html
@@ -8,7 +8,7 @@
     <title>Indexed Database Test</title>
 
     <script type="text/javascript;version=1.7">
-      function testSteps()
+      function* testSteps()
       {
         const name = window.location.pathname;
 
diff --git a/dom/indexedDB/test/browser_permissionsPromptDeny.js b/dom/indexedDB/test/browser_permissionsPromptDeny.js
index ce6760915ac5..4d8b4476b0d3 100644
--- a/dom/indexedDB/test/browser_permissionsPromptDeny.js
+++ b/dom/indexedDB/test/browser_permissionsPromptDeny.js
@@ -22,7 +22,7 @@ function promiseMessage(aMessage, browser) {
   });
 }
 
-add_task(function test1() {
+add_task(function* test1() {
   removePermission(testPageURL, "indexedDB");
 
   info("creating tab");
@@ -51,7 +51,7 @@ add_task(function test1() {
   gBrowser.removeCurrentTab();
 });
 
-add_task(function test2() {
+add_task(function* test2() {
   info("creating private window");
   let win = yield BrowserTestUtils.openNewBrowserWindow({ private : true });
   
@@ -81,7 +81,7 @@ add_task(function test2() {
   win.close();
 });
 
-add_task(function test3() {
+add_task(function* test3() {
   info("creating tab");
   gBrowser.selectedTab = gBrowser.addTab();
 
diff --git a/dom/indexedDB/test/chromeHelpers.js b/dom/indexedDB/test/chromeHelpers.js
index 16508f62a4c7..cba7011c104f 100644
--- a/dom/indexedDB/test/chromeHelpers.js
+++ b/dom/indexedDB/test/chromeHelpers.js
@@ -19,14 +19,14 @@ if (!window.runTest) {
 function finishTest()
 {
   SimpleTest.executeSoon(function() {
-    testGenerator.close();
+    testGenerator.return();
     SimpleTest.finish();
   });
 }
 
 function grabEventAndContinueHandler(event)
 {
-  testGenerator.send(event);
+  testGenerator.next(event);
 }
 
 function continueToNextStep()
diff --git a/dom/indexedDB/test/error_events_abort_transactions_iframe.html b/dom/indexedDB/test/error_events_abort_transactions_iframe.html
index fd0414975b00..41b5098e7cd0 100644
--- a/dom/indexedDB/test/error_events_abort_transactions_iframe.html
+++ b/dom/indexedDB/test/error_events_abort_transactions_iframe.html
@@ -21,7 +21,7 @@
     }
 
     function grabEventAndContinueHandler(event) {
-      testGenerator.send(event);
+      testGenerator.next(event);
     }
 
     function errorHandler(event) {
@@ -38,7 +38,6 @@
       // Let window.onerror have a chance to fire
       setTimeout(function() {
         setTimeout(function() {
-          testGenerator.close();
           window.parent.postMessage("SimpleTest.finish();", "*");
         }, 0);
       }, 0);
@@ -48,7 +47,7 @@
       is(message, "ConstraintError", "Expect a constraint error");
     };
 
-    function testSteps() {
+    function* testSteps() {
       window.parent.SpecialPowers.addPermission("indexedDB", true, document);
 
       let request = indexedDB.open(window.location.pathname, 1);
@@ -230,7 +229,6 @@
       event.preventDefault();
 
       finishTest();
-      yield undefined;
     }
   </script>
 
diff --git a/dom/indexedDB/test/event_propagation_iframe.html b/dom/indexedDB/test/event_propagation_iframe.html
index c571421c84c7..a93b765353c8 100644
--- a/dom/indexedDB/test/event_propagation_iframe.html
+++ b/dom/indexedDB/test/event_propagation_iframe.html
@@ -17,7 +17,7 @@
     }
 
     function grabEventAndContinueHandler(event) {
-      testGenerator.send(event);
+      testGenerator.next(event);
     }
 
     function errorHandler(event) {
@@ -29,7 +29,7 @@
       // Let window.onerror have a chance to fire
       setTimeout(function() {
         setTimeout(function() {
-          testGenerator.close();
+          testGenerator.return();
           ok(windowErrorCount == 1, "Good window.onerror count");
           window.parent.postMessage("SimpleTest.finish();", "*");
         }, 0);
@@ -86,7 +86,7 @@
       }
     }
 
-    function testSteps() {
+    function* testSteps() {
       window.parent.SpecialPowers.addPermission("indexedDB", true, document);
 
       let request = indexedDB.open(window.location.pathname, 1);
diff --git a/dom/indexedDB/test/exceptions_in_events_iframe.html b/dom/indexedDB/test/exceptions_in_events_iframe.html
index e8002d56c6a6..e3f9644da441 100644
--- a/dom/indexedDB/test/exceptions_in_events_iframe.html
+++ b/dom/indexedDB/test/exceptions_in_events_iframe.html
@@ -23,7 +23,7 @@
     }
 
     function grabEventAndContinueHandler(event) {
-      testGenerator.send(event);
+      testGenerator.next(event);
     }
 
     function errorHandler(event) {
@@ -40,7 +40,7 @@
       // Let window.onerror have a chance to fire
       setTimeout(function() {
         setTimeout(function() {
-          testGenerator.close();
+          testGenerator.return();
           window.parent.postMessage("SimpleTest.finish();", "*");
         }, 0);
       }, 0);
@@ -50,7 +50,7 @@
       return false;
     };
 
-    function testSteps() {
+    function* testSteps() {
       window.parent.SpecialPowers.addPermission("indexedDB", true, document);
 
       // Test 1: Throwing an exception in an upgradeneeded handler should
diff --git a/dom/indexedDB/test/file.js b/dom/indexedDB/test/file.js
index cc41f5b7a6c2..6c70eff1be25 100644
--- a/dom/indexedDB/test/file.js
+++ b/dom/indexedDB/test/file.js
@@ -90,7 +90,7 @@ function getWasmBinary(text)
 {
   let binary = getWasmBinarySync(text);
   SimpleTest.executeSoon(function() {
-    testGenerator.send(binary);
+    testGenerator.next(binary);
   });
 }
 
@@ -220,7 +220,7 @@ function verifyWasmModule(module1, module2)
 
 function grabFileUsageAndContinueHandler(request)
 {
-  testGenerator.send(request.fileUsage);
+  testGenerator.next(request.fileUsage);
 }
 
 function getUsage(usageHandler)
diff --git a/dom/indexedDB/test/helpers.js b/dom/indexedDB/test/helpers.js
index cc0b37d65226..80c5a37db0b8 100644
--- a/dom/indexedDB/test/helpers.js
+++ b/dom/indexedDB/test/helpers.js
@@ -46,7 +46,7 @@ testHarnessGenerator.next();
 
 function testHarnessSteps() {
   function nextTestHarnessStep(val) {
-    testHarnessGenerator.send(val);
+    testHarnessGenerator.next(val);
   }
 
   let testScriptPath;
@@ -222,8 +222,6 @@ function finishTest()
                                                "free");
 
   SimpleTest.executeSoon(function() {
-    testGenerator.close();
-    testHarnessGenerator.close();
     clearAllDatabases(function() { SimpleTest.finish(); });
   });
 }
@@ -235,12 +233,11 @@ function browserRunTest()
 
 function browserFinishTest()
 {
-  setTimeout(function() { testGenerator.close(); }, 0);
 }
 
 function grabEventAndContinueHandler(event)
 {
-  testGenerator.send(event);
+  testGenerator.next(event);
 }
 
 function continueToNextStep()
@@ -442,7 +439,7 @@ function workerScript() {
   };
 
   self.grabEventAndContinueHandler = function(_event_) {
-    testGenerator.send(_event_);
+    testGenerator.next(_event_);
   };
 
   self.continueToNextStep = function() {
@@ -608,7 +605,7 @@ function workerScript() {
 
       case "getWasmBinaryDone":
         info("Worker: get wasm binary done");
-        testGenerator.send(message.wasmBinary);
+        testGenerator.next(message.wasmBinary);
         break;
 
       default:
diff --git a/dom/indexedDB/test/test_bfcache.html b/dom/indexedDB/test/test_bfcache.html
index 5cb737384426..17089b5d041b 100644
--- a/dom/indexedDB/test/test_bfcache.html
+++ b/dom/indexedDB/test/test_bfcache.html
@@ -33,7 +33,7 @@
       }
     }
 
-    function testSteps()
+    function* testSteps()
     {
       var iframe = $("iframe");
       setCachePref(true);
@@ -53,7 +53,6 @@
 
       setCachePref(false);
       finishTest();
-      yield undefined;
     }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_blob_archive.html b/dom/indexedDB/test/test_blob_archive.html
index add1ad7ee42d..94fabb701ab8 100644
--- a/dom/indexedDB/test/test_blob_archive.html
+++ b/dom/indexedDB/test/test_blob_archive.html
@@ -11,7 +11,7 @@
 
   <script type="text/javascript;version=1.7">
 
-  function testSteps()
+  function* testSteps()
   {
     const BLOB_DATA =
       "504B03040A00000000002E6BF14000000000000000000000000005001C00746573742F" +
@@ -115,7 +115,6 @@
     ok(event.target.result == TEST_FILE_2_CONTENTS, "Correct text");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_blob_simple.html b/dom/indexedDB/test/test_blob_simple.html
index e7e4407197a9..c07f8e7a8667 100644
--- a/dom/indexedDB/test/test_blob_simple.html
+++ b/dom/indexedDB/test/test_blob_simple.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     info("Setting up test fixtures: create an IndexedDB database and object store.");
 
@@ -269,7 +269,6 @@
 
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_blob_worker_crash.html b/dom/indexedDB/test/test_blob_worker_crash.html
index 849915b863ee..6e105d0d7350 100644
--- a/dom/indexedDB/test/test_blob_worker_crash.html
+++ b/dom/indexedDB/test/test_blob_worker_crash.html
@@ -20,7 +20,7 @@
    * test.  Doing it out here is no good.
    */
 
-  function testSteps()
+  function* testSteps()
   {
     info("Open iframe, wait for it to do its IndexedDB stuff.");
 
@@ -49,7 +49,6 @@
     ok('Did not crash / trigger an assert!');
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_blob_worker_xhr_post.html b/dom/indexedDB/test/test_blob_worker_xhr_post.html
index a421c4256cef..481774e34473 100644
--- a/dom/indexedDB/test/test_blob_worker_xhr_post.html
+++ b/dom/indexedDB/test/test_blob_worker_xhr_post.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const BLOB_DATA = ["fun ", "times ", "all ", "around!"];
     const BLOB_TYPE = "text/plain";
@@ -101,7 +101,6 @@
     URL.revokeObjectURL(workerScriptUrl);
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_blob_worker_xhr_post_multifile.html b/dom/indexedDB/test/test_blob_worker_xhr_post_multifile.html
index c739d25860d5..0a463e7f3aa3 100644
--- a/dom/indexedDB/test/test_blob_worker_xhr_post_multifile.html
+++ b/dom/indexedDB/test/test_blob_worker_xhr_post_multifile.html
@@ -16,7 +16,7 @@
    * instead generate the expected 404.  This test is basically the same as
    * test_blob_worker_xhr_post.html except for the composite Blob.
    */
-  function testSteps()
+  function* testSteps()
   {
     const BLOB_DATA = ["fun ", "times ", "all ", "around!"];
     const BLOB_TYPE = "text/plain";
@@ -101,7 +101,6 @@
     URL.revokeObjectURL(workerScriptUrl);
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_blob_worker_xhr_read.html b/dom/indexedDB/test/test_blob_worker_xhr_read.html
index 920dbffae640..a29664678ec4 100644
--- a/dom/indexedDB/test/test_blob_worker_xhr_read.html
+++ b/dom/indexedDB/test/test_blob_worker_xhr_read.html
@@ -15,7 +15,7 @@
    * contents of the Blob from the worker using an XHR.  Ideally, we don't
    * deadlock the main thread.
    */
-  function testSteps()
+  function* testSteps()
   {
     const BLOB_DATA = ["Green"];
     const BLOB_TYPE = "text/plain";
@@ -102,7 +102,6 @@
     URL.revokeObjectURL(workerScriptUrl);
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_blob_worker_xhr_read_slice.html b/dom/indexedDB/test/test_blob_worker_xhr_read_slice.html
index 564b63f11673..afe154634847 100644
--- a/dom/indexedDB/test/test_blob_worker_xhr_read_slice.html
+++ b/dom/indexedDB/test/test_blob_worker_xhr_read_slice.html
@@ -16,7 +16,7 @@
    * (as of the time of writing this) basically the same as
    * test_blob_worker_xhr_read.html but with slicing added.
    */
-  function testSteps()
+  function* testSteps()
   {
     const BLOB_DATA = ["Green"];
     const BLOB_TYPE = "text/plain";
@@ -104,7 +104,6 @@
     URL.revokeObjectURL(workerScriptUrl);
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_file_array.html b/dom/indexedDB/test/test_file_array.html
index 580790d9736b..1a7128f16ecf 100644
--- a/dom/indexedDB/test/test_file_array.html
+++ b/dom/indexedDB/test/test_file_array.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -74,7 +74,6 @@
     is(bufferCache.length, 11, "Correct length");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_file_cross_database_copying.html b/dom/indexedDB/test/test_file_cross_database_copying.html
index bf65a3a6be04..767d79a55bfc 100644
--- a/dom/indexedDB/test/test_file_cross_database_copying.html
+++ b/dom/indexedDB/test/test_file_cross_database_copying.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const READ_WRITE = "readwrite";
 
@@ -95,7 +95,6 @@
     is(bufferCache.length, 2, "Correct length");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_file_delete.html b/dom/indexedDB/test/test_file_delete.html
index 8110c5a8c559..0892c9d7f93e 100644
--- a/dom/indexedDB/test/test_file_delete.html
+++ b/dom/indexedDB/test/test_file_delete.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const READ_WRITE = "readwrite";
 
@@ -124,7 +124,6 @@
     ok(!hasFileInfo(name, 3), "Correct ref count");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_file_os_delete.html b/dom/indexedDB/test/test_file_os_delete.html
index 62cbde837b5a..993a70fa4e8f 100644
--- a/dom/indexedDB/test/test_file_os_delete.html
+++ b/dom/indexedDB/test/test_file_os_delete.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const READ_WRITE = "readwrite";
 
@@ -96,7 +96,6 @@
     is(endUsage, startUsage, "OS files deleted");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_file_put_get_object.html b/dom/indexedDB/test/test_file_put_get_object.html
index 7b96f5687538..3b9fe80b7803 100644
--- a/dom/indexedDB/test/test_file_put_get_object.html
+++ b/dom/indexedDB/test/test_file_put_get_object.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const READ_WRITE = "readwrite";
 
@@ -77,7 +77,6 @@
     yield undefined;
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_file_put_get_values.html b/dom/indexedDB/test/test_file_put_get_values.html
index 3f18264d6e29..2f0cb7627796 100644
--- a/dom/indexedDB/test/test_file_put_get_values.html
+++ b/dom/indexedDB/test/test_file_put_get_values.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const READ_WRITE = "readwrite";
 
@@ -91,7 +91,6 @@
     is(bufferCache.length, 2, "Correct length");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_file_replace.html b/dom/indexedDB/test/test_file_replace.html
index a7cc5e6d02c1..2586bb99170c 100644
--- a/dom/indexedDB/test/test_file_replace.html
+++ b/dom/indexedDB/test/test_file_replace.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -57,7 +57,6 @@
     }
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_file_resurrection_delete.html b/dom/indexedDB/test/test_file_resurrection_delete.html
index e3d852929c83..35da0e0c42a7 100644
--- a/dom/indexedDB/test/test_file_resurrection_delete.html
+++ b/dom/indexedDB/test/test_file_resurrection_delete.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const READ_WRITE = "readwrite";
 
@@ -120,7 +120,6 @@
     is(getFileRefCount(name, 1), 0, "Correct ref count");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_file_resurrection_transaction_abort.html b/dom/indexedDB/test/test_file_resurrection_transaction_abort.html
index 1265833e43cc..498516d03681 100644
--- a/dom/indexedDB/test/test_file_resurrection_transaction_abort.html
+++ b/dom/indexedDB/test/test_file_resurrection_transaction_abort.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const READ_WRITE = "readwrite";
 
@@ -79,7 +79,6 @@
     is(getFileRefCount(name, 1), 0, "Correct ref count");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_file_sharing.html b/dom/indexedDB/test/test_file_sharing.html
index 2f03689f3d81..dd767d2881b7 100644
--- a/dom/indexedDB/test/test_file_sharing.html
+++ b/dom/indexedDB/test/test_file_sharing.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const READ_WRITE = "readwrite";
 
@@ -90,7 +90,6 @@
     is(bufferCache.length, 2, "Correct length");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_file_transaction_abort.html b/dom/indexedDB/test/test_file_transaction_abort.html
index 8c08c65177d2..882b3f8e8f73 100644
--- a/dom/indexedDB/test/test_file_transaction_abort.html
+++ b/dom/indexedDB/test/test_file_transaction_abort.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const READ_WRITE = "readwrite";
 
@@ -64,7 +64,6 @@
     ok(!hasFileInfo(name, 1), "Correct ref count");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_compat.html b/dom/indexedDB/test/test_filehandle_compat.html
index 667fcc99e5bf..b999d9267c4d 100644
--- a/dom/indexedDB/test/test_filehandle_compat.html
+++ b/dom/indexedDB/test/test_filehandle_compat.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -40,7 +40,6 @@
     event = yield undefined;
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_disabled_pref.html b/dom/indexedDB/test/test_filehandle_disabled_pref.html
index d695e10eeea8..b765320ceeae 100644
--- a/dom/indexedDB/test/test_filehandle_disabled_pref.html
+++ b/dom/indexedDB/test/test_filehandle_disabled_pref.html
@@ -13,7 +13,7 @@
     <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
     <script type="text/javascript;version=1.7">
-      function testSteps()
+      function* testSteps()
       {
         const databaseName = window.location.pathname;
         const databaseVersion = 1;
@@ -190,7 +190,6 @@
         yield undefined;
 
         finishTest();
-        yield undefined;
       }
     </script>
 
diff --git a/dom/indexedDB/test/test_filehandle_getFile.html b/dom/indexedDB/test/test_filehandle_getFile.html
index f17689f1de1d..bf2ee7737c92 100644
--- a/dom/indexedDB/test/test_filehandle_getFile.html
+++ b/dom/indexedDB/test/test_filehandle_getFile.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -41,7 +41,6 @@
     ok(request.onprogress === undefined, "Property should not exist");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_iteration.html b/dom/indexedDB/test/test_filehandle_iteration.html
index ebbc8b8beff0..927decb706e6 100644
--- a/dom/indexedDB/test/test_filehandle_iteration.html
+++ b/dom/indexedDB/test/test_filehandle_iteration.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const dbName = window.location.pathname;
     const dbVersion = 1;
@@ -65,7 +65,6 @@
     is(seenEntryCount, entryCount, "Correct entry count");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_lifetimes.html b/dom/indexedDB/test/test_filehandle_lifetimes.html
index 6e4946821394..16058bd8b3bb 100644
--- a/dom/indexedDB/test/test_filehandle_lifetimes.html
+++ b/dom/indexedDB/test/test_filehandle_lifetimes.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -45,7 +45,6 @@
     }
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_lifetimes_nested.html b/dom/indexedDB/test/test_filehandle_lifetimes_nested.html
index 78fc235e80b4..4e91eb82e5e8 100644
--- a/dom/indexedDB/test/test_filehandle_lifetimes_nested.html
+++ b/dom/indexedDB/test/test_filehandle_lifetimes_nested.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -57,7 +57,6 @@
     yield undefined;
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_location.html b/dom/indexedDB/test/test_filehandle_location.html
index 332fc9af1c0e..75498cee0b11 100644
--- a/dom/indexedDB/test/test_filehandle_location.html
+++ b/dom/indexedDB/test/test_filehandle_location.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -92,7 +92,6 @@
     is(fileHandle.location, 0, "Correct location");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_ordering.html b/dom/indexedDB/test/test_filehandle_ordering.html
index 0f402ed074f5..002e3400a639 100644
--- a/dom/indexedDB/test/test_filehandle_ordering.html
+++ b/dom/indexedDB/test/test_filehandle_ordering.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -50,7 +50,6 @@
     is(event.target.result, "2", "File handles were ordered properly.");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_overlapping.html b/dom/indexedDB/test/test_filehandle_overlapping.html
index 9f4cf8e6d501..a1e9db997079 100644
--- a/dom/indexedDB/test/test_filehandle_overlapping.html
+++ b/dom/indexedDB/test/test_filehandle_overlapping.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -61,7 +61,6 @@
     }
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_progress_events.html b/dom/indexedDB/test/test_filehandle_progress_events.html
index 0d2c7f7cbd39..e55bfc1aaf9d 100644
--- a/dom/indexedDB/test/test_filehandle_progress_events.html
+++ b/dom/indexedDB/test/test_filehandle_progress_events.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -66,7 +66,6 @@
     is(sum, testBuffer.byteLength, "Correct loaded progress sum");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_readonly_exceptions.html b/dom/indexedDB/test/test_filehandle_readonly_exceptions.html
index 566e5361b3cb..aa779543f10e 100644
--- a/dom/indexedDB/test/test_filehandle_readonly_exceptions.html
+++ b/dom/indexedDB/test/test_filehandle_readonly_exceptions.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -69,7 +69,6 @@
     }
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_request_readyState.html b/dom/indexedDB/test/test_filehandle_request_readyState.html
index d9cea030ce63..0e83fc45d846 100644
--- a/dom/indexedDB/test/test_filehandle_request_readyState.html
+++ b/dom/indexedDB/test/test_filehandle_request_readyState.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -57,7 +57,6 @@
     is(request.readyState, "done", "Correct readyState");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_serialization.html b/dom/indexedDB/test/test_filehandle_serialization.html
index 703a40e75acf..693436420b6a 100644
--- a/dom/indexedDB/test/test_filehandle_serialization.html
+++ b/dom/indexedDB/test/test_filehandle_serialization.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const READ_WRITE = "readwrite";
 
@@ -88,7 +88,6 @@
     }
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_store_snapshot.html b/dom/indexedDB/test/test_filehandle_store_snapshot.html
index 82d14256f26a..e855935f890d 100644
--- a/dom/indexedDB/test/test_filehandle_store_snapshot.html
+++ b/dom/indexedDB/test/test_filehandle_store_snapshot.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const READ_WRITE = "readwrite";
 
@@ -85,7 +85,6 @@
     yield undefined;
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_stream_tracking.html b/dom/indexedDB/test/test_filehandle_stream_tracking.html
index f85ff6fc3b5b..43cbb6303922 100644
--- a/dom/indexedDB/test/test_filehandle_stream_tracking.html
+++ b/dom/indexedDB/test/test_filehandle_stream_tracking.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -99,7 +99,6 @@
     ok(compareBuffers(resultBuffer2, testBuffer), "Correct data");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_success_events_after_abort.html b/dom/indexedDB/test/test_filehandle_success_events_after_abort.html
index 5b0c4de4e1fc..fd2388dd0446 100644
--- a/dom/indexedDB/test/test_filehandle_success_events_after_abort.html
+++ b/dom/indexedDB/test/test_filehandle_success_events_after_abort.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -62,7 +62,6 @@
     }
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_truncate.html b/dom/indexedDB/test/test_filehandle_truncate.html
index 4dfe331f3d4e..f74da6fa6aeb 100644
--- a/dom/indexedDB/test/test_filehandle_truncate.html
+++ b/dom/indexedDB/test/test_filehandle_truncate.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -78,7 +78,6 @@
     }
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_workers.html b/dom/indexedDB/test/test_filehandle_workers.html
index 24a8f920a630..3d1a44c1e5f0 100644
--- a/dom/indexedDB/test/test_filehandle_workers.html
+++ b/dom/indexedDB/test/test_filehandle_workers.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -136,7 +136,6 @@
     worker.terminate();
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_filehandle_write_read_data.html b/dom/indexedDB/test/test_filehandle_write_read_data.html
index 036d57117990..9ad513023f00 100644
--- a/dom/indexedDB/test/test_filehandle_write_read_data.html
+++ b/dom/indexedDB/test/test_filehandle_write_read_data.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -97,7 +97,6 @@
     is(result.size, location, "Correct size");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="file.js"></script>
diff --git a/dom/indexedDB/test/test_globalObjects_chrome.xul b/dom/indexedDB/test/test_globalObjects_chrome.xul
index 47e967d9692e..6e26e08a417c 100644
--- a/dom/indexedDB/test/test_globalObjects_chrome.xul
+++ b/dom/indexedDB/test/test_globalObjects_chrome.xul
@@ -13,7 +13,7 @@
 
   <script type="application/javascript;version=1.7">
   <![CDATA[
-  function testSteps() {
+  function* testSteps() {
     const name = window.location.pathname;
 
     // Test for IDBKeyRange and indexedDB availability in chrome windows.
diff --git a/dom/indexedDB/test/test_globalObjects_content.html b/dom/indexedDB/test/test_globalObjects_content.html
index 8a91a9ca3205..ba94befe0301 100644
--- a/dom/indexedDB/test/test_globalObjects_content.html
+++ b/dom/indexedDB/test/test_globalObjects_content.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     const name = window.location.pathname;
 
@@ -27,7 +27,6 @@
     ok(db, "Got database");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_globalObjects_other.xul b/dom/indexedDB/test/test_globalObjects_other.xul
index eb180a9b4a00..69a514e21890 100644
--- a/dom/indexedDB/test/test_globalObjects_other.xul
+++ b/dom/indexedDB/test/test_globalObjects_other.xul
@@ -13,7 +13,7 @@
 
   <script type="application/javascript;version=1.7">
   <![CDATA[
-  function testSteps() {
+  function* testSteps() {
     // Test for IDBKeyRange and indexedDB availability in bootstrap files.
     let test = Cc["@mozilla.org/dom/indexeddb/GlobalObjectsComponent;1"].
                createInstance(Ci.nsISupports).wrappedJSObject;
diff --git a/dom/indexedDB/test/test_leaving_page.html b/dom/indexedDB/test/test_leaving_page.html
index 6eb46f50ecc9..18e90ff878f6 100644
--- a/dom/indexedDB/test/test_leaving_page.html
+++ b/dom/indexedDB/test/test_leaving_page.html
@@ -19,7 +19,7 @@
       ok(false, "gotmessage: " + e.data);
     }
 
-    function testSteps()
+    function* testSteps()
     {
       var iframe = $("inner");
       iframe.src = "leaving_page_iframe.html";
@@ -42,7 +42,6 @@
       is(event.target.result.hello, "world", "second modification rolled back");
 
       finishTest();
-      yield undefined;
     }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_message_manager_ipc.html b/dom/indexedDB/test/test_message_manager_ipc.html
index f89cb9f89ac5..a7561b01b636 100644
--- a/dom/indexedDB/test/test_message_manager_ipc.html
+++ b/dom/indexedDB/test/test_message_manager_ipc.html
@@ -51,7 +51,7 @@ function childFrameScript() {
   }
 
   function grabAndContinue(arg) {
-    testGenerator.send(arg);
+    testGenerator.next(arg);
   }
 
   function errorHandler(event) {
@@ -61,7 +61,7 @@ function childFrameScript() {
     finish();
   }
 
-  function testSteps() {
+  function* testSteps() {
     addMessageListener(mmName, grabAndContinue);
     let message = yield undefined;
 
@@ -195,8 +195,6 @@ function childFrameScript() {
 
     info("Sending blob and slice from database to message manager");
     finish([blob, slice]);
-
-    yield undefined;
   }
 
   let testGenerator = testSteps();
@@ -211,10 +209,10 @@ function parentFrameScript(mm) {
   const blob = new Blob(blobData, { type: blobType });
 
   function grabAndContinue(arg) {
-    testGenerator.send(arg);
+    testGenerator.next(arg);
   }
 
-  function testSteps() {
+  function* testSteps() {
     let result = yield undefined;
 
     is(Array.isArray(result), true, "Child delivered an array of results");
@@ -264,7 +262,6 @@ function parentFrameScript(mm) {
     is(reader.result, blobData[0], "Second slice has correct data");
 
     SimpleTest.finish();
-    yield undefined;
   }
 
   let testGenerator = testSteps();
@@ -284,7 +281,7 @@ function parentFrameScript(mm) {
       }
 
       case "done": {
-        testGenerator.send(data.result);
+        testGenerator.next(data.result);
         break;
       }
 
diff --git a/dom/indexedDB/test/test_open_for_principal.html b/dom/indexedDB/test/test_open_for_principal.html
index 96bc2c43e481..bd6f401329ad 100644
--- a/dom/indexedDB/test/test_open_for_principal.html
+++ b/dom/indexedDB/test/test_open_for_principal.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-  function testSteps()
+  function* testSteps()
   {
     is("open" in indexedDB, true, "open() defined");
     is("openForPrincipal" in indexedDB, false, "openForPrincipal() not defined");
@@ -19,7 +19,6 @@
     is("deleteForPrincipal" in indexedDB, false, "deleteForPrincipal() not defined");
 
     finishTest();
-    yield undefined;
   }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/test_persistenceType.html b/dom/indexedDB/test/test_persistenceType.html
index cc44ffb777c6..4444115ce854 100644
--- a/dom/indexedDB/test/test_persistenceType.html
+++ b/dom/indexedDB/test/test_persistenceType.html
@@ -10,7 +10,7 @@
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
 
   <script type="text/javascript;version=1.7">
-    function testSteps()
+    function* testSteps()
     {
       const name = window.location.pathname;
       const version = 1;
@@ -81,7 +81,6 @@
       }
 
       finishTest();
-      yield undefined;
     }
   </script>
   <script type="text/javascript;version=1.7" src="helpers.js"></script>
diff --git a/dom/indexedDB/test/unit/test_abort_deleted_index.js b/dom/indexedDB/test/unit/test_abort_deleted_index.js
index 8bd1f6ae2cac..1bd6816d7a95 100644
--- a/dom/indexedDB/test/unit/test_abort_deleted_index.js
+++ b/dom/indexedDB/test/unit/test_abort_deleted_index.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const storeName = "test store";
@@ -74,5 +74,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_abort_deleted_objectStore.js b/dom/indexedDB/test/unit/test_abort_deleted_objectStore.js
index 98035b3dab72..5086c3476275 100644
--- a/dom/indexedDB/test/unit/test_abort_deleted_objectStore.js
+++ b/dom/indexedDB/test/unit/test_abort_deleted_objectStore.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const storeName_ToBeDeleted = "test store to be deleted";
@@ -70,5 +70,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_add_put.js b/dom/indexedDB/test/unit/test_add_put.js
index 923d19d7e443..3ab0aa121cb7 100644
--- a/dom/indexedDB/test/unit/test_add_put.js
+++ b/dom/indexedDB/test/unit/test_add_put.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   let openRequest = indexedDB.open(name, 1);
@@ -161,5 +161,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_add_twice_failure.js b/dom/indexedDB/test/unit/test_add_twice_failure.js
index 80a4e5c55d7b..37b18911e138 100644
--- a/dom/indexedDB/test/unit/test_add_twice_failure.js
+++ b/dom/indexedDB/test/unit/test_add_twice_failure.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -38,6 +38,5 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_advance.js b/dom/indexedDB/test/unit/test_advance.js
index 3187a8f5e59e..a8b0fd71a7fa 100644
--- a/dom/indexedDB/test/unit/test_advance.js
+++ b/dom/indexedDB/test/unit/test_advance.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const dataCount = 30;
 
@@ -188,5 +188,4 @@ function testSteps()
   is(count, dataCount - 1, "Saw all data");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_autoIncrement.js b/dom/indexedDB/test/unit/test_autoIncrement.js
index f2ea0982232a..c3266aefabee 100644
--- a/dom/indexedDB/test/unit/test_autoIncrement.js
+++ b/dom/indexedDB/test/unit/test_autoIncrement.js
@@ -33,7 +33,7 @@ function genCheck(key, value, test, options) {
   }
 }
 
-function testSteps()
+function* testSteps()
 {
   const dbname = this.window ? window.location.pathname : "Splendid Test";
   const RW = "readwrite";
@@ -396,5 +396,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_autoIncrement_indexes.js b/dom/indexedDB/test/unit/test_autoIncrement_indexes.js
index ce2d5d55279d..8e79f53fa71d 100644
--- a/dom/indexedDB/test/unit/test_autoIncrement_indexes.js
+++ b/dom/indexedDB/test/unit/test_autoIncrement_indexes.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   let request = indexedDB.open(this.window ? window.location.pathname : "Splendid Test", 1);
   request.onerror = errorHandler;
@@ -52,5 +52,4 @@ function testSteps()
   is (event.target.result.id, 1, "Entry in third");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_blob_file_backed.js b/dom/indexedDB/test/unit/test_blob_file_backed.js
index 664c9e2c94c8..7a0d1f5ae359 100644
--- a/dom/indexedDB/test/unit/test_blob_file_backed.js
+++ b/dom/indexedDB/test/unit/test_blob_file_backed.js
@@ -7,7 +7,7 @@ var disableWorkerTest = "This test uses SpecialPowers";
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const fileData = "abcdefghijklmnopqrstuvwxyz";
   const fileType = "text/plain";
@@ -74,5 +74,4 @@ function testSteps()
   is(fileReader.result, fileData, "Correct data");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_blocked_order.js b/dom/indexedDB/test/unit/test_blocked_order.js
index 1c70853f4f00..68fb336ace82 100644
--- a/dom/indexedDB/test/unit/test_blocked_order.js
+++ b/dom/indexedDB/test/unit/test_blocked_order.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const databaseName =
     ("window" in this) ? window.location.pathname : "Test";
@@ -175,5 +175,4 @@ function testSteps()
   // Just allow this to remain blocked ...
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_cleanup_transaction.js b/dom/indexedDB/test/unit/test_cleanup_transaction.js
index 070e9015eba2..d21b871fc2a1 100644
--- a/dom/indexedDB/test/unit/test_cleanup_transaction.js
+++ b/dom/indexedDB/test/unit/test_cleanup_transaction.js
@@ -77,11 +77,11 @@ function testSteps()
       trans.oncomplete = function(event) {
         i++;
         j++;
-        testGenerator.send(true);
+        testGenerator.next(true);
       }
       trans.onabort = function(event) {
         is(trans.error.name, "QuotaExceededError", "Reached quota limit");
-        testGenerator.send(false);
+        testGenerator.next(false);
       }
 
       let completeFired = yield undefined;
diff --git a/dom/indexedDB/test/unit/test_clear.js b/dom/indexedDB/test/unit/test_clear.js
index acce5c261fc9..039bea0cea4c 100644
--- a/dom/indexedDB/test/unit/test_clear.js
+++ b/dom/indexedDB/test/unit/test_clear.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const entryCount = 1000;
@@ -93,5 +93,4 @@ function testSteps()
   isnot(event.target.result, firstKey, "Got a different key");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_complex_keyPaths.js b/dom/indexedDB/test/unit/test_complex_keyPaths.js
index 24375813d559..1bb1948998a3 100644
--- a/dom/indexedDB/test/unit/test_complex_keyPaths.js
+++ b/dom/indexedDB/test/unit/test_complex_keyPaths.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   // Test object stores
 
@@ -262,5 +262,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_count.js b/dom/indexedDB/test/unit/test_count.js
index 32ba5e95016b..a0026a3a22a0 100644
--- a/dom/indexedDB/test/unit/test_count.js
+++ b/dom/indexedDB/test/unit/test_count.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreName = "People";
@@ -350,5 +350,4 @@ function testSteps()
      "Correct number of index entries for bound keyRange");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_create_index.js b/dom/indexedDB/test/unit/test_create_index.js
index 284cca2b38ac..1b3e0a262b80 100644
--- a/dom/indexedDB/test/unit/test_create_index.js
+++ b/dom/indexedDB/test/unit/test_create_index.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreInfo = [
@@ -117,5 +117,4 @@ function testSteps()
   event = yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_create_index_with_integer_keys.js b/dom/indexedDB/test/unit/test_create_index_with_integer_keys.js
index d14b5041192e..0c1c592a08f8 100644
--- a/dom/indexedDB/test/unit/test_create_index_with_integer_keys.js
+++ b/dom/indexedDB/test/unit/test_create_index_with_integer_keys.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const data = { id: new Date().getTime(),
                  num: parseInt(Math.random() * 1000) };
@@ -62,5 +62,4 @@ function testSteps()
   is(seenCount, 1, "Saw our entry");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_create_locale_aware_index.js b/dom/indexedDB/test/unit/test_create_locale_aware_index.js
index 7fc7a4ab52d1..952952382e14 100644
--- a/dom/indexedDB/test/unit/test_create_locale_aware_index.js
+++ b/dom/indexedDB/test/unit/test_create_locale_aware_index.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreInfo = [
@@ -119,5 +119,4 @@ function testSteps()
   event = yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_create_objectStore.js b/dom/indexedDB/test/unit/test_create_objectStore.js
index 215723c26920..b7aad66ef5a4 100644
--- a/dom/indexedDB/test/unit/test_create_objectStore.js
+++ b/dom/indexedDB/test/unit/test_create_objectStore.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreInfo = [
@@ -130,5 +130,4 @@ function testSteps()
   event = yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_cursor_mutation.js b/dom/indexedDB/test/unit/test_cursor_mutation.js
index 13e859891c1d..250be2a9b97b 100644
--- a/dom/indexedDB/test/unit/test_cursor_mutation.js
+++ b/dom/indexedDB/test/unit/test_cursor_mutation.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const objectStoreData = [
     // This one will be removed.
@@ -113,6 +113,4 @@ function testSteps()
   finishTest();
 
   objectStore = null; // Bug 943409 workaround.
-
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_cursor_update_updates_indexes.js b/dom/indexedDB/test/unit/test_cursor_update_updates_indexes.js
index 1ea0bc88371d..bb2beb5aab61 100644
--- a/dom/indexedDB/test/unit/test_cursor_update_updates_indexes.js
+++ b/dom/indexedDB/test/unit/test_cursor_update_updates_indexes.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const START_DATA = "hi";
@@ -94,6 +94,5 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_cursors.js b/dom/indexedDB/test/unit/test_cursors.js
index 48d1eff83390..2fec3c326aae 100644
--- a/dom/indexedDB/test/unit/test_cursors.js
+++ b/dom/indexedDB/test/unit/test_cursors.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const keys = [1, -1, 0, 10, 2000, "q", "z", "two", "b", "a"];
@@ -379,5 +379,4 @@ function testSteps()
   db.close();
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_database_onclose.js b/dom/indexedDB/test/unit/test_database_onclose.js
index 28650d835cca..36d3b47a81fb 100644
--- a/dom/indexedDB/test/unit/test_database_onclose.js
+++ b/dom/indexedDB/test/unit/test_database_onclose.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   function testInvalidStateError(aDb, aTxn) {
     try {
@@ -105,10 +105,10 @@ function testSteps()
     addRequest.onerror = function(event) {
       info("addRequest.onerror, objectId: " + objectId);
       txn.onerror = grabEventAndContinueHandler;
-      testGenerator.send(true);
+      testGenerator.next(true);
     }
     addRequest.onsuccess = function() {
-      testGenerator.send(false);
+      testGenerator.next(false);
     }
 
     if (objectId == 0) {
@@ -170,7 +170,7 @@ function testSteps()
     let addRequest = objectStore.add({foo: "foo"});
     addRequest.onsuccess = function() {
       objectId++;
-      testGenerator.send(objectId == numberOfObjects);
+      testGenerator.next(objectId == numberOfObjects);
     }
     addRequest.onerror = errorHandler;
 
@@ -196,7 +196,7 @@ function testSteps()
   let readRequest = objectStore.openCursor();
   readRequest.onerror = function(event) {
     info("readRequest.onerror, numberOfReadObjects: " + numberOfReadObjects);
-    testGenerator.send(true);
+    testGenerator.next(true);
   }
   readRequest.onsuccess = function(event) {
     let cursor = event.target.result;
@@ -206,7 +206,7 @@ function testSteps()
     } else {
       info("Cursor is invalid, numberOfReadObjects: " + numberOfReadObjects);
       todo(false, "All records are iterated before database is cleared!");
-      testGenerator.send(false);
+      testGenerator.next(false);
     }
   }
 
@@ -241,5 +241,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_deleteDatabase.js b/dom/indexedDB/test/unit/test_deleteDatabase.js
index 7c9f76522580..7bd62a5ddba2 100644
--- a/dom/indexedDB/test/unit/test_deleteDatabase.js
+++ b/dom/indexedDB/test/unit/test_deleteDatabase.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -102,5 +102,4 @@ function testSteps()
   ok(true, "after deleting a non-existent database, open should work");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_deleteDatabase_interactions.js b/dom/indexedDB/test/unit/test_deleteDatabase_interactions.js
index 87f6a6d20869..b339a9113663 100644
--- a/dom/indexedDB/test/unit/test_deleteDatabase_interactions.js
+++ b/dom/indexedDB/test/unit/test_deleteDatabase_interactions.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -58,5 +58,4 @@ function testSteps()
   is(event.target.result.objectStoreNames.length, 0, "DB should have no object stores");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_deleteDatabase_onblocked.js b/dom/indexedDB/test/unit/test_deleteDatabase_onblocked.js
index 51390612d7c0..6cea4b7864ec 100644
--- a/dom/indexedDB/test/unit/test_deleteDatabase_onblocked.js
+++ b/dom/indexedDB/test/unit/test_deleteDatabase_onblocked.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const dbVersion = 10;
@@ -79,5 +79,4 @@ function testSteps()
   db.close();
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_deleteDatabase_onblocked_duringVersionChange.js b/dom/indexedDB/test/unit/test_deleteDatabase_onblocked_duringVersionChange.js
index 40ece64c0da0..e0a05d92e4bc 100644
--- a/dom/indexedDB/test/unit/test_deleteDatabase_onblocked_duringVersionChange.js
+++ b/dom/indexedDB/test/unit/test_deleteDatabase_onblocked_duringVersionChange.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const dbVersion = 10;
@@ -80,5 +80,4 @@ function testSteps()
   db.close();
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_event_source.js b/dom/indexedDB/test/unit/test_event_source.js
index 232a13f0dce1..53e9b0983b13 100644
--- a/dom/indexedDB/test/unit/test_event_source.js
+++ b/dom/indexedDB/test/unit/test_event_source.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreName = "Objects";
@@ -32,5 +32,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_filehandle_append_read_data.js b/dom/indexedDB/test/unit/test_filehandle_append_read_data.js
index ed2f77ef6c15..96b696363add 100644
--- a/dom/indexedDB/test/unit/test_filehandle_append_read_data.js
+++ b/dom/indexedDB/test/unit/test_filehandle_append_read_data.js
@@ -7,7 +7,7 @@ var disableWorkerTest = "FileHandle doesn't work in workers yet";
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -94,5 +94,4 @@ function testSteps()
   is(result.size, location, "Correct size");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_getAll.js b/dom/indexedDB/test/unit/test_getAll.js
index c543feb07755..7a0bfdebaa42 100644
--- a/dom/indexedDB/test/unit/test_getAll.js
+++ b/dom/indexedDB/test/unit/test_getAll.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -191,5 +191,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_global_data.js b/dom/indexedDB/test/unit/test_global_data.js
index e7df96ec9450..b9f1c3fd4865 100644
--- a/dom/indexedDB/test/unit/test_global_data.js
+++ b/dom/indexedDB/test/unit/test_global_data.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStore =  { name: "Objects",
@@ -53,5 +53,4 @@ function testSteps()
   is(objectStore1.keyPath, objectStore2.keyPath, "Same keyPath");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_index_empty_keyPath.js b/dom/indexedDB/test/unit/test_index_empty_keyPath.js
index 9fbcfc9c9701..3a14792e6ea2 100644
--- a/dom/indexedDB/test/unit/test_index_empty_keyPath.js
+++ b/dom/indexedDB/test/unit/test_index_empty_keyPath.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -33,7 +33,7 @@ function testSteps()
     request.onerror = errorHandler;
     request.onsuccess = function(event) {
       if (++addedData == objectStoreData.length) {
-        testGenerator.send(event);
+        testGenerator.next(event);
       }
     }
   }
@@ -79,5 +79,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_index_getAll.js b/dom/indexedDB/test/unit/test_index_getAll.js
index b4af8fd049f3..49340ae8efb2 100644
--- a/dom/indexedDB/test/unit/test_index_getAll.js
+++ b/dom/indexedDB/test/unit/test_index_getAll.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreName = "People";
@@ -69,7 +69,7 @@ function testSteps()
     request.onerror = errorHandler;
     request.onsuccess = function(event) {
       if (++addedData == objectStoreData.length) {
-        testGenerator.send(event);
+        testGenerator.next(event);
       }
     }
   }
@@ -187,5 +187,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_index_getAllObjects.js b/dom/indexedDB/test/unit/test_index_getAllObjects.js
index 1aad5dc08bb1..d557ff71fe43 100644
--- a/dom/indexedDB/test/unit/test_index_getAllObjects.js
+++ b/dom/indexedDB/test/unit/test_index_getAllObjects.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreName = "People";
@@ -69,7 +69,7 @@ function testSteps()
     request.onerror = errorHandler;
     request.onsuccess = function(event) {
       if (++addedData == objectStoreData.length) {
-        testGenerator.send(event);
+        testGenerator.next(event);
       }
     }
   }
@@ -229,5 +229,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_index_object_cursors.js b/dom/indexedDB/test/unit/test_index_object_cursors.js
index f3daa433b656..49b3dcd3ab80 100644
--- a/dom/indexedDB/test/unit/test_index_object_cursors.js
+++ b/dom/indexedDB/test/unit/test_index_object_cursors.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const objectStoreData = [
     { name: "", options: { keyPath: "id", autoIncrement: true } },
@@ -143,5 +143,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_index_update_delete.js b/dom/indexedDB/test/unit/test_index_update_delete.js
index 860087aadf73..272f0340a2d0 100644
--- a/dom/indexedDB/test/unit/test_index_update_delete.js
+++ b/dom/indexedDB/test/unit/test_index_update_delete.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   let name = this.window ? window.location.pathname : "Splendid Test";
   let request = indexedDB.open(name, 1);
@@ -167,5 +167,4 @@ function testSteps()
 
   finishTest();
   event = db = request = null; // Bug 943409 workaround.
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_indexes.js b/dom/indexedDB/test/unit/test_indexes.js
index aaf536febe4d..405dcfd21f50 100644
--- a/dom/indexedDB/test/unit/test_indexes.js
+++ b/dom/indexedDB/test/unit/test_indexes.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -69,7 +69,7 @@ function testSteps()
     request.onerror = errorHandler;
     request.onsuccess = function(event) {
       if (++addedData == objectStoreData.length) {
-        testGenerator.send(event);
+        testGenerator.next(event);
       }
     }
   }
@@ -1257,5 +1257,4 @@ function testSteps()
   is(keyIndex, objectStoreDataNameSort.length, "Saw all the expected keys");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_indexes_bad_values.js b/dom/indexedDB/test/unit/test_indexes_bad_values.js
index 37817c28673c..076b4c1ab7a4 100644
--- a/dom/indexedDB/test/unit/test_indexes_bad_values.js
+++ b/dom/indexedDB/test/unit/test_indexes_bad_values.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -55,7 +55,7 @@ function testSteps()
     request.onerror = errorHandler;
     request.onsuccess = function(event) {
       if (++addedData == objectStoreData.length) {
-        testGenerator.send(event);
+        testGenerator.next(event);
       }
     }
   }
@@ -126,5 +126,4 @@ function testSteps()
      "Saw all people");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_indexes_funny_things.js b/dom/indexedDB/test/unit/test_indexes_funny_things.js
index af0384c7719f..d2fe400a9f03 100644
--- a/dom/indexedDB/test/unit/test_indexes_funny_things.js
+++ b/dom/indexedDB/test/unit/test_indexes_funny_things.js
@@ -5,12 +5,12 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   // Blob constructor is not implemented outside of windows yet (Bug 827723).
   if (!this.window) {
     finishTest();
-    yield undefined;
+    return;
   }
 
   const name = this.window ? window.location.pathname : "Splendid Test";
@@ -65,7 +65,7 @@ function testSteps()
     request.onerror = errorHandler;
     request.onsuccess = function(event) {
       if (++addedData == objectStoreData.length) {
-        testGenerator.send(event);
+        testGenerator.next(event);
       }
     }
   }
@@ -164,5 +164,4 @@ function testSteps()
   is(keyIndex, objectStoreDataLengthSort.length, "Saw all the expected keys");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_invalid_cursor.js b/dom/indexedDB/test/unit/test_invalid_cursor.js
index 11fba36545ea..435a7d8193f2 100644
--- a/dom/indexedDB/test/unit/test_invalid_cursor.js
+++ b/dom/indexedDB/test/unit/test_invalid_cursor.js
@@ -7,7 +7,7 @@ var disableWorkerTest = "Need to implement a gc() function for worker tests";
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const dbName = ("window" in this) ? window.location.pathname : "test";
   const dbVersion = 1;
@@ -60,5 +60,4 @@ function testSteps()
   is(event.target.result, null, "No more entries");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_invalid_version.js b/dom/indexedDB/test/unit/test_invalid_version.js
index 7566fad8abed..118001988c15 100644
--- a/dom/indexedDB/test/unit/test_invalid_version.js
+++ b/dom/indexedDB/test/unit/test_invalid_version.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -46,5 +46,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_key_requirements.js b/dom/indexedDB/test/unit/test_key_requirements.js
index 90f3ce864c46..80fc18515460 100644
--- a/dom/indexedDB/test/unit/test_key_requirements.js
+++ b/dom/indexedDB/test/unit/test_key_requirements.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps(); 
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -281,5 +281,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_keys.js b/dom/indexedDB/test/unit/test_keys.js
index 00072748e0ef..02b50bf12872 100644
--- a/dom/indexedDB/test/unit/test_keys.js
+++ b/dom/indexedDB/test/unit/test_keys.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const dbname = this.window ? window.location.pathname : "Splendid Test";
   const RW = "readwrite"
@@ -265,5 +265,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_locale_aware_index_getAll.js b/dom/indexedDB/test/unit/test_locale_aware_index_getAll.js
index c59bc127c7af..dbbd61887101 100644
--- a/dom/indexedDB/test/unit/test_locale_aware_index_getAll.js
+++ b/dom/indexedDB/test/unit/test_locale_aware_index_getAll.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreName = "People";
@@ -69,7 +69,7 @@ function testSteps()
     request.onerror = errorHandler;
     request.onsuccess = function(event) {
       if (++addedData == objectStoreData.length) {
-        testGenerator.send(event);
+        testGenerator.next(event);
       }
     }
   }
@@ -187,5 +187,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_locale_aware_index_getAllObjects.js b/dom/indexedDB/test/unit/test_locale_aware_index_getAllObjects.js
index 1ec82f1c21b7..33da821deb14 100644
--- a/dom/indexedDB/test/unit/test_locale_aware_index_getAllObjects.js
+++ b/dom/indexedDB/test/unit/test_locale_aware_index_getAllObjects.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreName = "People";
@@ -69,7 +69,7 @@ function testSteps()
     request.onerror = errorHandler;
     request.onsuccess = function(event) {
       if (++addedData == objectStoreData.length) {
-        testGenerator.send(event);
+        testGenerator.next(event);
       }
     }
   }
@@ -229,5 +229,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_locale_aware_indexes.js b/dom/indexedDB/test/unit/test_locale_aware_indexes.js
index b79ca58c7682..f09ad8e21f91 100644
--- a/dom/indexedDB/test/unit/test_locale_aware_indexes.js
+++ b/dom/indexedDB/test/unit/test_locale_aware_indexes.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -69,7 +69,7 @@ function testSteps()
     request.onerror = errorHandler;
     request.onsuccess = function(event) {
       if (++addedData == objectStoreData.length) {
-        testGenerator.send(event);
+        testGenerator.next(event);
       }
     }
   }
@@ -1264,5 +1264,4 @@ function testSteps()
   is(keyIndex, objectStoreDataNameSort.length, "Saw all the expected keys");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_lowDiskSpace.js b/dom/indexedDB/test/unit/test_lowDiskSpace.js
index eaea5797dffe..31431d457356 100644
--- a/dom/indexedDB/test/unit/test_lowDiskSpace.js
+++ b/dom/indexedDB/test/unit/test_lowDiskSpace.js
@@ -10,7 +10,7 @@ var self = this;
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const dbName = self.window ? window.location.pathname : "test_lowDiskSpace";
   const dbVersion = 1;
@@ -715,7 +715,6 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
 
 function RequestCounter(expectedType) {
diff --git a/dom/indexedDB/test/unit/test_maximal_serialized_object_size.js b/dom/indexedDB/test/unit/test_maximal_serialized_object_size.js
index 12a933ddcd8d..328d435ece30 100644
--- a/dom/indexedDB/test/unit/test_maximal_serialized_object_size.js
+++ b/dom/indexedDB/test/unit/test_maximal_serialized_object_size.js
@@ -7,7 +7,7 @@ var disableWorkerTest = "Need a way to set temporary prefs from a worker";
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ?
     window.location.pathname : "test_maximal_serialized_object_size.js";
@@ -91,5 +91,4 @@ function testSteps()
   db.close();
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_multientry.js b/dom/indexedDB/test/unit/test_multientry.js
index c1479498ea78..00acfd722b41 100644
--- a/dom/indexedDB/test/unit/test_multientry.js
+++ b/dom/indexedDB/test/unit/test_multientry.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   // Test object stores
   
@@ -214,5 +214,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_names_sorted.js b/dom/indexedDB/test/unit/test_names_sorted.js
index eac03a84a649..b8dec4e61b18 100644
--- a/dom/indexedDB/test/unit/test_names_sorted.js
+++ b/dom/indexedDB/test/unit/test_names_sorted.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreInfo = [
@@ -110,5 +110,4 @@ function testSteps()
   db.close();
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_objectCursors.js b/dom/indexedDB/test/unit/test_objectCursors.js
index 6c84a7394913..3d3ed2f7bb10 100644
--- a/dom/indexedDB/test/unit/test_objectCursors.js
+++ b/dom/indexedDB/test/unit/test_objectCursors.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -80,6 +80,5 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_objectStore_getAllKeys.js b/dom/indexedDB/test/unit/test_objectStore_getAllKeys.js
index dfc1870c7f02..5c21e8acd134 100644
--- a/dom/indexedDB/test/unit/test_objectStore_getAllKeys.js
+++ b/dom/indexedDB/test/unit/test_objectStore_getAllKeys.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps() {
+function* testSteps() {
   const dbName = this.window ?
                  window.location.pathname :
                  "test_objectStore_getAllKeys";
@@ -119,5 +119,4 @@ function testSteps() {
   is(event.target.result.length, 0, "Got correct array length");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_objectStore_inline_autoincrement_key_added_on_put.js b/dom/indexedDB/test/unit/test_objectStore_inline_autoincrement_key_added_on_put.js
index 176b3962d294..cab52c8b09b3 100644
--- a/dom/indexedDB/test/unit/test_objectStore_inline_autoincrement_key_added_on_put.js
+++ b/dom/indexedDB/test/unit/test_objectStore_inline_autoincrement_key_added_on_put.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -50,6 +50,5 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_objectStore_openKeyCursor.js b/dom/indexedDB/test/unit/test_objectStore_openKeyCursor.js
index 3e88cedb508f..e1713ad9f21d 100644
--- a/dom/indexedDB/test/unit/test_objectStore_openKeyCursor.js
+++ b/dom/indexedDB/test/unit/test_objectStore_openKeyCursor.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps() {
+function* testSteps() {
   const dbName = this.window ?
                  window.location.pathname :
                  "test_objectStore_openKeyCursor";
@@ -396,5 +396,4 @@ function testSteps() {
   ok(match, "All keys matched");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_objectStore_remove_values.js b/dom/indexedDB/test/unit/test_objectStore_remove_values.js
index ee0628e9d025..ee858bba4aaf 100644
--- a/dom/indexedDB/test/unit/test_objectStore_remove_values.js
+++ b/dom/indexedDB/test/unit/test_objectStore_remove_values.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -87,6 +87,5 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_object_identity.js b/dom/indexedDB/test/unit/test_object_identity.js
index fa7b91339c56..eba403f3b565 100644
--- a/dom/indexedDB/test/unit/test_object_identity.js
+++ b/dom/indexedDB/test/unit/test_object_identity.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   let request = indexedDB.open(this.window ? window.location.pathname : "Splendid Test", 1);
   request.onerror = errorHandler;
@@ -43,6 +43,5 @@ function testSteps()
   ok(index4 !== index2, "Different indexes");
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_odd_result_order.js b/dom/indexedDB/test/unit/test_odd_result_order.js
index fb3d992c92c3..9ff2254a7d68 100644
--- a/dom/indexedDB/test/unit/test_odd_result_order.js
+++ b/dom/indexedDB/test/unit/test_odd_result_order.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const data = { key: 5, index: 10 };
 
@@ -72,5 +72,4 @@ function testSteps()
   ok(key === undefined, "Got the right value");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_open_empty_db.js b/dom/indexedDB/test/unit/test_open_empty_db.js
index add9566693b2..97a2c279b627 100644
--- a/dom/indexedDB/test/unit/test_open_empty_db.js
+++ b/dom/indexedDB/test/unit/test_open_empty_db.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const names = [
     //"",
@@ -41,6 +41,5 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_open_objectStore.js b/dom/indexedDB/test/unit/test_open_objectStore.js
index 207107941c3a..91f0fc78b0b7 100644
--- a/dom/indexedDB/test/unit/test_open_objectStore.js
+++ b/dom/indexedDB/test/unit/test_open_objectStore.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreName = "Objects";
@@ -34,6 +34,5 @@ function testSteps()
   if(objectStore.indexNames.length, 0, "Bad indexNames");
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_optionalArguments.js b/dom/indexedDB/test/unit/test_optionalArguments.js
index ad170dc8d789..032a1ecdabeb 100644
--- a/dom/indexedDB/test/unit/test_optionalArguments.js
+++ b/dom/indexedDB/test/unit/test_optionalArguments.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const osName = "people";
   const indexName = "weight";
@@ -1706,6 +1706,5 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_overlapping_transactions.js b/dom/indexedDB/test/unit/test_overlapping_transactions.js
index 2606d7aea518..ea2d59f8a2eb 100644
--- a/dom/indexedDB/test/unit/test_overlapping_transactions.js
+++ b/dom/indexedDB/test/unit/test_overlapping_transactions.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStores = [ "foo", "bar" ];
@@ -87,6 +87,5 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_put_get_values.js b/dom/indexedDB/test/unit/test_put_get_values.js
index b7345795ca17..90c5d50e7d3c 100644
--- a/dom/indexedDB/test/unit/test_put_get_values.js
+++ b/dom/indexedDB/test/unit/test_put_get_values.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreName = "Objects";
@@ -50,6 +50,5 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_put_get_values_autoIncrement.js b/dom/indexedDB/test/unit/test_put_get_values_autoIncrement.js
index 3291148d35de..843841c2a019 100644
--- a/dom/indexedDB/test/unit/test_put_get_values_autoIncrement.js
+++ b/dom/indexedDB/test/unit/test_put_get_values_autoIncrement.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreName = "Objects";
@@ -50,5 +50,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_quotaExceeded_recovery.js b/dom/indexedDB/test/unit/test_quotaExceeded_recovery.js
index 1f04bb6d032b..4ba7c77c4b6b 100644
--- a/dom/indexedDB/test/unit/test_quotaExceeded_recovery.js
+++ b/dom/indexedDB/test/unit/test_quotaExceeded_recovery.js
@@ -87,11 +87,11 @@ function testSteps()
           i++;
         }
         j++;
-        testGenerator.send(true);
+        testGenerator.next(true);
       }
       trans.onabort = function(event) {
         is(trans.error.name, "QuotaExceededError", "Reached quota limit");
-        testGenerator.send(false);
+        testGenerator.next(false);
       }
 
       let completeFired = yield undefined;
diff --git a/dom/indexedDB/test/unit/test_readonly_transactions.js b/dom/indexedDB/test/unit/test_readonly_transactions.js
index 91f0f4c9a1be..d08a51b0f2bf 100644
--- a/dom/indexedDB/test/unit/test_readonly_transactions.js
+++ b/dom/indexedDB/test/unit/test_readonly_transactions.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const osName = "foo";
@@ -170,5 +170,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_readwriteflush_disabled.js b/dom/indexedDB/test/unit/test_readwriteflush_disabled.js
index 484b1aa42963..bca5e9e79657 100644
--- a/dom/indexedDB/test/unit/test_readwriteflush_disabled.js
+++ b/dom/indexedDB/test/unit/test_readwriteflush_disabled.js
@@ -7,7 +7,7 @@ var disableWorkerTest = "Need a way to set temporary prefs from a worker";
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name =
     this.window ? window.location.pathname : "test_readwriteflush_disabled.js";
@@ -68,5 +68,4 @@ function testSteps()
      "exception has the correct message");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_remove_index.js b/dom/indexedDB/test/unit/test_remove_index.js
index d9916b97594d..4aa13c31962c 100644
--- a/dom/indexedDB/test/unit/test_remove_index.js
+++ b/dom/indexedDB/test/unit/test_remove_index.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const indexName = "My Test Index";
@@ -54,5 +54,4 @@ function testSteps()
   event = yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_remove_objectStore.js b/dom/indexedDB/test/unit/test_remove_objectStore.js
index 324fa0d2f1af..8a830364a3d2 100644
--- a/dom/indexedDB/test/unit/test_remove_objectStore.js
+++ b/dom/indexedDB/test/unit/test_remove_objectStore.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const objectStoreName = "Objects";
@@ -85,7 +85,7 @@ function testSteps()
   request.onerror = errorHandler;
   request.onsuccess = function(event) {
     is(event.target.result, null, "ObjectStore shouldn't have any items");
-    testGenerator.send(event);
+    testGenerator.next(event);
   }
   event = yield undefined;
 
@@ -125,5 +125,4 @@ function testSteps()
   event = yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_rename_index.js b/dom/indexedDB/test/unit/test_rename_index.js
index e7ab8c03828c..84ccbf86fb86 100644
--- a/dom/indexedDB/test/unit/test_rename_index.js
+++ b/dom/indexedDB/test/unit/test_rename_index.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const storeName = "test store";
@@ -189,5 +189,4 @@ function testSteps()
   db.close();
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_rename_index_errors.js b/dom/indexedDB/test/unit/test_rename_index_errors.js
index cac972a1fa55..873b35c4baa0 100644
--- a/dom/indexedDB/test/unit/test_rename_index_errors.js
+++ b/dom/indexedDB/test/unit/test_rename_index_errors.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const storeName = "test store";
@@ -125,5 +125,4 @@ function testSteps()
   db.close();
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_rename_objectStore.js b/dom/indexedDB/test/unit/test_rename_objectStore.js
index 4c7796889ef7..b5bfe6cc0854 100644
--- a/dom/indexedDB/test/unit/test_rename_objectStore.js
+++ b/dom/indexedDB/test/unit/test_rename_objectStore.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const storeName_ToBeDeleted = "test store to be deleted";
@@ -167,5 +167,4 @@ function testSteps()
   db.close();
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_rename_objectStore_errors.js b/dom/indexedDB/test/unit/test_rename_objectStore_errors.js
index 0e4b796a6627..0e6fc8b17bc2 100644
--- a/dom/indexedDB/test/unit/test_rename_objectStore_errors.js
+++ b/dom/indexedDB/test/unit/test_rename_objectStore_errors.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
   const storeName1 = "test store 1";
@@ -123,5 +123,4 @@ function testSteps()
   db.close();
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_request_readyState.js b/dom/indexedDB/test/unit/test_request_readyState.js
index c19d974a3f71..e9fb36b1cfd2 100644
--- a/dom/indexedDB/test/unit/test_request_readyState.js
+++ b/dom/indexedDB/test/unit/test_request_readyState.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -47,5 +47,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_setVersion.js b/dom/indexedDB/test/unit/test_setVersion.js
index cb2400b5d375..1d8d7ab8318a 100644
--- a/dom/indexedDB/test/unit/test_setVersion.js
+++ b/dom/indexedDB/test/unit/test_setVersion.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -46,6 +46,5 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_setVersion_abort.js b/dom/indexedDB/test/unit/test_setVersion_abort.js
index 262c10346401..b19f7923285a 100644
--- a/dom/indexedDB/test/unit/test_setVersion_abort.js
+++ b/dom/indexedDB/test/unit/test_setVersion_abort.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -93,5 +93,4 @@ function testSteps()
   is(objectStore.indexNames.length, 0, "Correct indexNames length still");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_setVersion_events.js b/dom/indexedDB/test/unit/test_setVersion_events.js
index 1bd757dc8802..431a4a2c720b 100644
--- a/dom/indexedDB/test/unit/test_setVersion_events.js
+++ b/dom/indexedDB/test/unit/test_setVersion_events.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -160,6 +160,5 @@ function testSteps()
   is(event.newVersion, 2, "Correct new version");
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_setVersion_exclusion.js b/dom/indexedDB/test/unit/test_setVersion_exclusion.js
index 2a51ab0909d2..bedb51988747 100644
--- a/dom/indexedDB/test/unit/test_setVersion_exclusion.js
+++ b/dom/indexedDB/test/unit/test_setVersion_exclusion.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -91,5 +91,4 @@ function testSteps()
   is(db.version, 2, "Database has correct version");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_setVersion_throw.js b/dom/indexedDB/test/unit/test_setVersion_throw.js
index a589bb385115..c3eb1f114c6b 100644
--- a/dom/indexedDB/test/unit/test_setVersion_throw.js
+++ b/dom/indexedDB/test/unit/test_setVersion_throw.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "test_setVersion_throw";
 
@@ -50,5 +50,4 @@ function testSteps()
   is(event.target.error.name, "AbortError", "Request has AbortError");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_storage_manager_estimate.js b/dom/indexedDB/test/unit/test_storage_manager_estimate.js
index 0e3dc2d351be..829c3af88da2 100644
--- a/dom/indexedDB/test/unit/test_storage_manager_estimate.js
+++ b/dom/indexedDB/test/unit/test_storage_manager_estimate.js
@@ -1,6 +1,6 @@
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname :
 	       "test_storage_manager_estimate.js";
@@ -13,7 +13,7 @@ function testSteps()
      'estimate() method exists and returns a Promise');
 
   navigator.storage.estimate().then(estimation => {
-    testGenerator.send(estimation.usage);
+    testGenerator.next(estimation.usage);
   });
 
   let before = yield undefined;
@@ -31,7 +31,7 @@ function testSteps()
   yield undefined;
 
   navigator.storage.estimate().then(estimation => {
-    testGenerator.send(estimation.usage);
+    testGenerator.next(estimation.usage);
   });
   let usageAfterCreate = yield undefined;
   ok(usageAfterCreate > before, 'estimated usage must increase after createObjectStore');
@@ -45,14 +45,13 @@ function testSteps()
   event = yield undefined;
 
   navigator.storage.estimate().then(estimation => {
-    testGenerator.send(estimation.usage);
+    testGenerator.next(estimation.usage);
   });
   let usageAfterPut = yield undefined;
   ok(usageAfterPut > usageAfterCreate, 'estimated usage must increase after putting large object');
   db.close();
 
   finishTest();
-  yield undefined;
 }
 
 function setup()
diff --git a/dom/indexedDB/test/unit/test_success_events_after_abort.js b/dom/indexedDB/test/unit/test_success_events_after_abort.js
index efd138370703..da9f48efbca3 100644
--- a/dom/indexedDB/test/unit/test_success_events_after_abort.js
+++ b/dom/indexedDB/test/unit/test_success_events_after_abort.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   let request = indexedDB.open(this.window ? window.location.pathname : "Splendid Test", 1);
   request.onerror = errorHandler;
@@ -55,6 +55,5 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_table_locks.js b/dom/indexedDB/test/unit/test_table_locks.js
index 900f78edf3ab..e3021a60dc34 100644
--- a/dom/indexedDB/test/unit/test_table_locks.js
+++ b/dom/indexedDB/test/unit/test_table_locks.js
@@ -17,7 +17,7 @@ const loopCount = 100;
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   let req = indexedDB.open(dbName, dbVersion);
   req.onerror = errorHandler;
@@ -57,7 +57,6 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
 
 function doReadOnlyTransaction(db, key, remaining)
diff --git a/dom/indexedDB/test/unit/test_table_rollback.js b/dom/indexedDB/test/unit/test_table_rollback.js
index afe194ad5217..b2d07ffe172c 100644
--- a/dom/indexedDB/test/unit/test_table_rollback.js
+++ b/dom/indexedDB/test/unit/test_table_rollback.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const dbName = ("window" in this) ? window.location.pathname : "test";
   const objName1 = "foo";
@@ -111,5 +111,4 @@ function testSteps()
   is(writeAborted, true, "Aborted readwrite transaction");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_temporary_storage.js b/dom/indexedDB/test/unit/test_temporary_storage.js
index 15426abbb55f..e175a1c4a755 100644
--- a/dom/indexedDB/test/unit/test_temporary_storage.js
+++ b/dom/indexedDB/test/unit/test_temporary_storage.js
@@ -50,7 +50,7 @@ function testSteps()
            gotUpgradeIncomplete ? "AbortError" : "QuotaExceededError",
            "Reached quota limit");
         event.preventDefault();
-        testGenerator.send(false);
+        testGenerator.next(false);
       }
       request.onupgradeneeded = function(event) {
         event.target.transaction.onabort = function(e) {
@@ -65,7 +65,7 @@ function testSteps()
         let db = event.target.result;
         is(db.version, finalVersion, "Correct version " + finalVersion);
         databases.push(db);
-        testGenerator.send(true);
+        testGenerator.next(true);
       }
 
       let shouldContinue = yield undefined;
@@ -97,7 +97,7 @@ function testSteps()
            gotUpgradeIncomplete ? "AbortError" : "QuotaExceededError",
            "Reached quota limit");
         event.preventDefault();
-        testGenerator.send(false);
+        testGenerator.next(false);
       }
       request.onupgradeneeded = function(event) {
         event.target.transaction.onabort = function(e) {
@@ -112,7 +112,7 @@ function testSteps()
         let db = event.target.result;
         is(db.version, finalVersion, "Correct version " + finalVersion);
         databases.push(db);
-        testGenerator.send(true);
+        testGenerator.next(true);
       }
 
       let shouldContinue = yield undefined;
diff --git a/dom/indexedDB/test/unit/test_traffic_jam.js b/dom/indexedDB/test/unit/test_traffic_jam.js
index f09985b1338d..0c37b230f6fe 100644
--- a/dom/indexedDB/test/unit/test_traffic_jam.js
+++ b/dom/indexedDB/test/unit/test_traffic_jam.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -82,6 +82,5 @@ function testSteps()
   event.target.result.close();
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_transaction_abort.js b/dom/indexedDB/test/unit/test_transaction_abort.js
index 0f051f968e80..4b2eaff2cd27 100644
--- a/dom/indexedDB/test/unit/test_transaction_abort.js
+++ b/dom/indexedDB/test/unit/test_transaction_abort.js
@@ -13,7 +13,7 @@ function abortListener(evt)
   is(evt.target.error, null, "Expect a null error for an aborted transaction");
 }
 
-function testSteps()
+function* testSteps()
 {
   const name = this.window ? window.location.pathname : "Splendid Test";
 
@@ -380,5 +380,4 @@ function testSteps()
   ok(abortFired, "Abort should have fired!");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_transaction_abort_hang.js b/dom/indexedDB/test/unit/test_transaction_abort_hang.js
index cb59174f6a22..388626c32e5f 100644
--- a/dom/indexedDB/test/unit/test_transaction_abort_hang.js
+++ b/dom/indexedDB/test/unit/test_transaction_abort_hang.js
@@ -8,7 +8,7 @@ var self = this;
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const dbName = self.window ?
                  window.location.pathname :
@@ -87,5 +87,4 @@ function testSteps()
   ok(caughtError, "Caught the error event when we aborted the transaction");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_transaction_duplicate_store_names.js b/dom/indexedDB/test/unit/test_transaction_duplicate_store_names.js
index f37b14bab383..b2bbe38588cd 100644
--- a/dom/indexedDB/test/unit/test_transaction_duplicate_store_names.js
+++ b/dom/indexedDB/test/unit/test_transaction_duplicate_store_names.js
@@ -6,7 +6,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps() {
+function* testSteps() {
   const dbName = this.window ?
                  window.location.pathname :
                  "test_transaction_duplicate_store_names";
@@ -39,5 +39,4 @@ function testSteps() {
   ok(true, "Transaction created successfully");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_transaction_error.js b/dom/indexedDB/test/unit/test_transaction_error.js
index 14217eba8a56..d3912b48cc09 100644
--- a/dom/indexedDB/test/unit/test_transaction_error.js
+++ b/dom/indexedDB/test/unit/test_transaction_error.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps() {
+function* testSteps() {
   const dbName = this.window ?
                  window.location.pathname :
                  "test_transaction_error";
@@ -132,5 +132,4 @@ function testSteps() {
      "Transaction has correct error");
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_transaction_lifetimes.js b/dom/indexedDB/test/unit/test_transaction_lifetimes.js
index e42f7a2188cd..6817d06ba946 100644
--- a/dom/indexedDB/test/unit/test_transaction_lifetimes.js
+++ b/dom/indexedDB/test/unit/test_transaction_lifetimes.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   let request = indexedDB.open(this.window ? window.location.pathname : "Splendid Test", 1);
   request.onerror = errorHandler;
@@ -87,5 +87,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_transaction_lifetimes_nested.js b/dom/indexedDB/test/unit/test_transaction_lifetimes_nested.js
index 5d63945ba987..0c182607aa0e 100644
--- a/dom/indexedDB/test/unit/test_transaction_lifetimes_nested.js
+++ b/dom/indexedDB/test/unit/test_transaction_lifetimes_nested.js
@@ -7,7 +7,7 @@ var disableWorkerTest = "This test uses SpecialPowers";
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   let request = indexedDB.open(this.window ? window.location.pathname : "Splendid Test", 1);
   request.onerror = errorHandler;
@@ -48,5 +48,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_transaction_ordering.js b/dom/indexedDB/test/unit/test_transaction_ordering.js
index 5e3c2fd742ae..6bdcda25f168 100644
--- a/dom/indexedDB/test/unit/test_transaction_ordering.js
+++ b/dom/indexedDB/test/unit/test_transaction_ordering.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   let request = indexedDB.open(this.window ? window.location.pathname : "Splendid Test", 1);
   request.onerror = errorHandler;
@@ -44,6 +44,5 @@ function testSteps()
   is(event.target.result, "2", "Transactions were ordered properly.");
 
   finishTest();
-  yield undefined;
 }
 
diff --git a/dom/indexedDB/test/unit/test_unique_index_update.js b/dom/indexedDB/test/unit/test_unique_index_update.js
index 97caef3249d9..749986eca1a0 100644
--- a/dom/indexedDB/test/unit/test_unique_index_update.js
+++ b/dom/indexedDB/test/unit/test_unique_index_update.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   let request = indexedDB.open(this.window ? window.location.pathname : "Splendid Test", 1);
   request.onerror = errorHandler;
@@ -60,5 +60,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_view_put_get_values.js b/dom/indexedDB/test/unit/test_view_put_get_values.js
index 7f3cdf3fe0f1..2dad2f64c653 100644
--- a/dom/indexedDB/test/unit/test_view_put_get_values.js
+++ b/dom/indexedDB/test/unit/test_view_put_get_values.js
@@ -7,7 +7,7 @@ var disableWorkerTest = "Need a way to set temporary prefs from a worker";
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name =
     this.window ? window.location.pathname : "test_view_put_get_values.js";
@@ -98,5 +98,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_wasm_getAll.js b/dom/indexedDB/test/unit/test_wasm_getAll.js
index 5d933f44eb43..1bc2208db054 100644
--- a/dom/indexedDB/test/unit/test_wasm_getAll.js
+++ b/dom/indexedDB/test/unit/test_wasm_getAll.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name =
     this.window ? window.location.pathname : "test_wasm_getAll.js";
@@ -16,7 +16,7 @@ function testSteps()
 
   if (!isWasmSupported()) {
     finishTest();
-    yield undefined;
+    return;
   }
 
   getWasmBinary('(module (func (result i32) (i32.const 1)))');
@@ -119,5 +119,4 @@ function testSteps()
   }
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/test_wasm_put_get_values.js b/dom/indexedDB/test/unit/test_wasm_put_get_values.js
index f2bcf1ca0356..c38e5d9e5a36 100644
--- a/dom/indexedDB/test/unit/test_wasm_put_get_values.js
+++ b/dom/indexedDB/test/unit/test_wasm_put_get_values.js
@@ -5,7 +5,7 @@
 
 var testGenerator = testSteps();
 
-function testSteps()
+function* testSteps()
 {
   const name =
     this.window ? window.location.pathname : "test_wasm_put_get_values.js";
@@ -16,7 +16,7 @@ function testSteps()
 
   if (!isWasmSupported()) {
     finishTest();
-    yield undefined;
+    return;
   }
 
   getWasmBinary('(module (func (nop)))');
@@ -76,5 +76,4 @@ function testSteps()
   yield undefined;
 
   finishTest();
-  yield undefined;
 }
diff --git a/dom/indexedDB/test/unit/xpcshell-head-parent-process.js b/dom/indexedDB/test/unit/xpcshell-head-parent-process.js
index 6c99e7be8731..d6caf0a42b70 100644
--- a/dom/indexedDB/test/unit/xpcshell-head-parent-process.js
+++ b/dom/indexedDB/test/unit/xpcshell-head-parent-process.js
@@ -74,14 +74,13 @@ function finishTest()
   SpecialPowers.removeFiles();
 
   do_execute_soon(function(){
-    testGenerator.close();
     do_test_finished();
   })
 }
 
 function grabEventAndContinueHandler(event)
 {
-  testGenerator.send(event);
+  testGenerator.next(event);
 }
 
 function continueToNextStep()
@@ -392,7 +391,7 @@ function getWasmBinary(text)
 {
   let binary = getWasmBinarySync(text);
   executeSoon(function() {
-    testGenerator.send(binary);
+    testGenerator.next(binary);
   });
 }
 
@@ -500,7 +499,7 @@ function verifyWasmModule(module1, module2)
 
 function grabFileUsageAndContinueHandler(request)
 {
-  testGenerator.send(request.fileUsage);
+  testGenerator.next(request.fileUsage);
 }
 
 function getUsage(usageHandler)
diff --git a/dom/ipc/tests/test_blob_sliced_from_parent_process.html b/dom/ipc/tests/test_blob_sliced_from_parent_process.html
index 7d8a1665f184..b234464962f2 100644
--- a/dom/ipc/tests/test_blob_sliced_from_parent_process.html
+++ b/dom/ipc/tests/test_blob_sliced_from_parent_process.html
@@ -45,10 +45,10 @@ function childFrameScript() {
   }
 
   function grabAndContinue(arg) {
-    testGenerator.send(arg);
+    testGenerator.next(arg);
   }
 
-  function testSteps() {
+  function* testSteps() {
     addMessageListener(messageName, grabAndContinue);
     let message = yield undefined;
 
@@ -98,8 +98,6 @@ function childFrameScript() {
 
     info("Sending second slice");
     finish(slice);
-
-    yield undefined;
   }
 
   let testGenerator = testSteps();
@@ -115,10 +113,10 @@ function parentFrameScript(mm) {
   const sliceText = "an";
 
   function grabAndContinue(arg) {
-    testGenerator.send(arg);
+    testGenerator.next(arg);
   }
 
-  function testSteps() {
+  function* testSteps() {
     let slice = yield undefined;
 
     ok(slice instanceof Blob, "Received a Blob");
@@ -132,8 +130,6 @@ function parentFrameScript(mm) {
 
     is(reader.result, sliceText, "Slice has correct data");
     SimpleTest.finish();
-
-    yield undefined;
   }
 
   let testGenerator = testSteps();
@@ -153,7 +149,7 @@ function parentFrameScript(mm) {
       }
 
       case "done": {
-        testGenerator.send(data.result);
+        testGenerator.next(data.result);
         break;
       }
 
diff --git a/dom/security/test/contentverifier/head.js b/dom/security/test/contentverifier/head.js
index c997f64a573f..b356534016b4 100644
--- a/dom/security/test/contentverifier/head.js
+++ b/dom/security/test/contentverifier/head.js
@@ -72,7 +72,7 @@ function pushPrefs(...aPrefs) {
 /*
  * run tests with input from TESTS
  */
-function doTest(aExpectedStrings, reload, aUrl, aNewTabPref) {
+function* doTest(aExpectedStrings, reload, aUrl, aNewTabPref) {
   // set about:newtab location for this test if it's a newtab test
   if (aNewTabPref) {
     aboutNewTabService.newTabURL = aNewTabPref;
@@ -186,7 +186,7 @@ function doTest(aExpectedStrings, reload, aUrl, aNewTabPref) {
   );
 }
 
-function runTests() {
+function* runTests() {
   // run tests from TESTS
   for (let i = 0; i < TESTS.length; i++) {
     let testCase = TESTS[i];
@@ -203,6 +203,6 @@ function runTests() {
       url = testCase.url;
     }
 
-    yield doTest(aExpectedStrings, reload, url, aNewTabPref);
+    yield* doTest(aExpectedStrings, reload, url, aNewTabPref);
   }
 }
diff --git a/dom/security/test/cors/test_CrossSiteXHR.html b/dom/security/test/cors/test_CrossSiteXHR.html
index 714fb2868fb4..8b921b2ba2de 100644
--- a/dom/security/test/cors/test_CrossSiteXHR.html
+++ b/dom/security/test/cors/test_CrossSiteXHR.html
@@ -30,7 +30,7 @@ function initTest() {
 
 function initTestCallback() {
   window.addEventListener("message", function(e) {
-    gen.send(e.data);
+    gen.next(e.data);
   }, false);
 
   gen = runTest();
@@ -38,7 +38,7 @@ function initTestCallback() {
   gen.next()
 }
 
-function runTest() {
+function* runTest() {
   var loader = document.getElementById('loader');
   var loaderWindow = loader.contentWindow;
   loader.onload = function () { gen.next() };
@@ -1451,8 +1451,6 @@ function runTest() {
 
 
   SimpleTest.finish();
-
-  yield undefined;
 }
 
 </script>
diff --git a/dom/security/test/cors/test_CrossSiteXHR_cache.html b/dom/security/test/cors/test_CrossSiteXHR_cache.html
index 3252eff4a54b..d53877ebdc84 100644
--- a/dom/security/test/cors/test_CrossSiteXHR_cache.html
+++ b/dom/security/test/cors/test_CrossSiteXHR_cache.html
@@ -20,12 +20,12 @@ SimpleTest.waitForExplicitFinish();
 SimpleTest.requestFlakyTimeout("This test needs to generate artificial pauses, hence it uses timeouts.  There is no way around it, unfortunately. :(");
 
 window.addEventListener("message", function(e) {
-  gen.send(e.data);
+  gen.next(e.data);
 }, false);
 
 gen = runTest();
 
-function runTest() {
+function* runTest() {
   var loader = document.getElementById('loader');
   var loaderWindow = loader.contentWindow;
   loader.onload = function () { gen.next() };
@@ -577,8 +577,6 @@ function runTest() {
   }
 
   SimpleTest.finish();
-
-  yield undefined;
 }
 
 </script>
diff --git a/dom/security/test/cors/test_CrossSiteXHR_origin.html b/dom/security/test/cors/test_CrossSiteXHR_origin.html
index 1012ae5933c0..e70aad5cb364 100644
--- a/dom/security/test/cors/test_CrossSiteXHR_origin.html
+++ b/dom/security/test/cors/test_CrossSiteXHR_origin.html
@@ -51,12 +51,12 @@ var origins =
    //['https://sub1.test1.example.com:443'],
 
 window.addEventListener("message", function(e) {
-  gen.send(e.data);
+  gen.next(e.data);
 }, false);
 
 gen = runTest();
 
-function runTest() {
+function* runTest() {
   var loader = document.getElementById('loader');
   var loaderWindow = loader.contentWindow;
   loader.onload = function () { gen.next() };
@@ -159,8 +159,6 @@ function runTest() {
   }
 
   SimpleTest.finish();
-
-  yield undefined;
 }
 
 addLoadEvent(function() {
diff --git a/dom/tests/browser/browser_bug1008941_dismissGeolocationHanger.js b/dom/tests/browser/browser_bug1008941_dismissGeolocationHanger.js
index 93b2124ef082..3d2686868e66 100644
--- a/dom/tests/browser/browser_bug1008941_dismissGeolocationHanger.js
+++ b/dom/tests/browser/browser_bug1008941_dismissGeolocationHanger.js
@@ -7,7 +7,7 @@
 const TEST_URI = "http://example.com/" +
                  "browser/dom/tests/browser/position.html";
 
-add_task(function testDismissHanger() {
+add_task(function* testDismissHanger() {
   info("Check that location is not shared when dismissing the geolocation hanger");
 
   let promisePanelShown = BrowserTestUtils.waitForEvent(PopupNotifications.panel, "popupshown", true);
diff --git a/dom/tests/mochitest/general/test_bug504220.html b/dom/tests/mochitest/general/test_bug504220.html
index a88180c89aa5..10918b2a3044 100644
--- a/dom/tests/mochitest/general/test_bug504220.html
+++ b/dom/tests/mochitest/general/test_bug504220.html
@@ -40,7 +40,7 @@ function run_test() {
 
   SimpleTest.waitForExplicitFinish();
 
-  function waitForHashchange() {
+  function* waitForHashchange() {
     // Change the document's hash.  If we've been running this test manually,
     // the hash might already be "#foo", so we need to check in order to be
     // sure we trigger a hashchange.
@@ -53,7 +53,6 @@ function run_test() {
 
     is(numEvents, 1, "Exactly one hashchange should have been fired.");
     SimpleTest.finish();
-    yield undefined;
   }
 
   var gGen = waitForHashchange();
diff --git a/dom/tests/mochitest/general/test_domWindowUtils.html b/dom/tests/mochitest/general/test_domWindowUtils.html
index 377900c8088b..9a70a82f4cd5 100644
--- a/dom/tests/mochitest/general/test_domWindowUtils.html
+++ b/dom/tests/mochitest/general/test_domWindowUtils.html
@@ -37,7 +37,7 @@ var gTests = [
                                  in boolean aIgnoreRootScrollFrame,
                                  in boolean aFlushLayout);
 */
-function testElementFromPoint() {
+async function testElementFromPoint() {
   let onscreen = document.getElementById("onscreen");
   let offscreen = document.getElementById("offscreen");
   let htmldoc = document.documentElement;
@@ -89,105 +89,84 @@ function testElementFromPoint() {
                                      x, y, ignoreScroll, flushLayout));
     is(found, expected, "at index " + i + " for data " + testData[i][0].toSource());
   }
-
-  SimpleTest.executeSoon(function() {
-    next();
-  });
 },
 
 /**
  * Test .isHandlingUserInput attribute.
  */
-function testHandlingUserInput() {
+async function testHandlingUserInput() {
   ok('isHandlingUserInput' in domWindowUtils,
      "isHandlingUserInput should be present");
 
   is(domWindowUtils.isHandlingUserInput, false,
      "isHandlingUserInput should return false if nothing is happening");
 
-  function testEvents() {
-    var data = [
-      {
-        eventName: "click",
-        result: true,
-      },
-      {
-        eventName: "mousemove",
-        result: false,
-      },
-      {
-        eventName: "mouseup",
-        result: true,
-      },
-      {
-        eventName: "mousedown",
-        result: true,
-      },
-      {
-        eventName: "keydown",
-        result: true,
-      },
-      {
-        eventName: "keyup",
-        result: true,
-      },
-    ];
+  var data = [
+    {
+      eventName: "click",
+      result: true,
+    },
+    {
+      eventName: "mousemove",
+      result: false,
+    },
+    {
+      eventName: "mouseup",
+      result: true,
+    },
+    {
+      eventName: "mousedown",
+      result: true,
+    },
+    {
+      eventName: "keydown",
+      result: true,
+    },
+    {
+      eventName: "keyup",
+      result: true,
+    },
+  ];
 
-    for (let i=0; i<data.length; ++i) {
+  for (let i=0; i<data.length; ++i) {
+    let eventPromise = new Promise(resolve => {
       document.addEventListener(data[i].eventName, function() {
-        document.removeEventListener(data[i].eventName, arguments.callee);
-
         is(domWindowUtils.isHandlingUserInput, data[i].result,
            "isHandlingUserInput should be " + data[i].result);
 
-        SimpleTest.executeSoon(function() {
-          try { testEventsRunner.next(); } catch (e) { }
-        });
-      });
-
-      SimpleTest.executeSoon(function() {
-        if (data[i].eventName == "click") {
-          synthesizeMouseAtCenter(document.body, {});
-        } else if (data[i].eventName.indexOf("key") == 0) {
-          synthesizeKey("VK_A", { type: data[i].eventName });
-        } else {
-          synthesizeMouseAtCenter(document.body, { type: data[i].eventName });
-        }
-      });
-
-      yield undefined;
-    }
+        SimpleTest.executeSoon(resolve);
+      }, {once: true});
+    });
 
     SimpleTest.executeSoon(function() {
-      next();
+      if (data[i].eventName == "click") {
+        synthesizeMouseAtCenter(document.body, {});
+      } else if (data[i].eventName.indexOf("key") == 0) {
+        synthesizeKey("VK_A", { type: data[i].eventName });
+      } else {
+        synthesizeMouseAtCenter(document.body, { type: data[i].eventName });
+      }
     });
-  }
 
-  var testEventsRunner = testEvents();
-  testEventsRunner.next();
+    await eventPromise;
+  }
 },
 ];
 
-function runner() {
+async function runner() {
   for (let i=0; i<gTests.length; ++i) {
-    gTests[i]();
-    yield undefined;
+    if (i > 0) {
+      await new Promise(r => SimpleTest.executeSoon(r));
+    }
+    await gTests[i]();
   }
 
   SimpleTest.finish();
 };
 
-var gTestRunner = runner();
-
-function next() {
-  try { gTestRunner.next(); } catch (e) { if (e != StopIteration) { throw e; } }
-}
-
 // Run the test from onload, since the onscreen and offscreen divs should be in
 // the right places by then.
-addLoadEvent(function() {
-  gTestRunner.next();
-});
+addLoadEvent(runner);
 
 </script>
 
diff --git a/dom/tests/mochitest/general/test_spacetopagedown.html b/dom/tests/mochitest/general/test_spacetopagedown.html
index 03f840f3d687..9a4ac0ed6e9a 100644
--- a/dom/tests/mochitest/general/test_spacetopagedown.html
+++ b/dom/tests/mochitest/general/test_spacetopagedown.html
@@ -28,7 +28,7 @@ function initTest()
 
 function runTest()
 {
-  Task.async(function () {
+  Task.async(function* () {
     yield pressKey(false);
 
     ok(window.scrollY > 0, "Space with no focus" + window.scrollY);
diff --git a/dom/tests/mochitest/storageevent/test_storageNotifications.html b/dom/tests/mochitest/storageevent/test_storageNotifications.html
index eff416937a2c..6e0e2b2cca2c 100644
--- a/dom/tests/mochitest/storageevent/test_storageNotifications.html
+++ b/dom/tests/mochitest/storageevent/test_storageNotifications.html
@@ -34,7 +34,7 @@ function setup() {
   });
 }
 
-function Tests()
+function* Tests()
 {
   // Initially check the both storages are empty
   is(sessionStorage.length, 0, "Session storage is empty [1]");
diff --git a/dom/tests/mochitest/whatwg/postMessage_structured_clone_helper.html b/dom/tests/mochitest/whatwg/postMessage_structured_clone_helper.html
index b3cdfac2f4f5..e983b4dc2283 100644
--- a/dom/tests/mochitest/whatwg/postMessage_structured_clone_helper.html
+++ b/dom/tests/mochitest/whatwg/postMessage_structured_clone_helper.html
@@ -5,7 +5,7 @@
   <script type="application/javascript;version=1.7"
           src="postMessage_structured_clone_helper.js"></script>
   <script type="application/javascript;version=1.7">
-    var generator = new getTestContent()
+    var generator = getTestContent()
 
     function isClone(a, b) {
         window.dump("Object a: " + a + "\n");
@@ -93,7 +93,7 @@
 
     function receiveMessage(evt)
     {
-      if (isClone(evt.data, generator.next()))
+      if (isClone(evt.data, generator.next().value))
         window.parent.postMessage("TEST-PASS", "*");
       else
         window.parent.postMessage("TEST-FAIL", "*");
diff --git a/dom/tests/mochitest/whatwg/postMessage_structured_clone_helper.js b/dom/tests/mochitest/whatwg/postMessage_structured_clone_helper.js
index d56bc329880a..9d1fdff856d7 100644
--- a/dom/tests/mochitest/whatwg/postMessage_structured_clone_helper.js
+++ b/dom/tests/mochitest/whatwg/postMessage_structured_clone_helper.js
@@ -1,4 +1,4 @@
-function getTestContent()
+function* getTestContent()
 {
   yield "hello";
   yield 2+3;
diff --git a/dom/tests/mochitest/whatwg/test_postMessage_structured_clone.html b/dom/tests/mochitest/whatwg/test_postMessage_structured_clone.html
index ec09412277db..971553f13bbe 100644
--- a/dom/tests/mochitest/whatwg/test_postMessage_structured_clone.html
+++ b/dom/tests/mochitest/whatwg/test_postMessage_structured_clone.html
@@ -29,25 +29,27 @@ SimpleTest.waitForExplicitFinish();
 
 var lastMessage = null;
 var crossOrigin = false;
-var generator = new getTestContent();
+var generator = getTestContent();
 
 function runNextSameOrigin() {
-  try {
-    lastMessage = generator.next();
-  } catch (e) {
-    generator = new getTestContent();
+  let {done, value} = generator.next();
+  if (done) {
+    generator = getTestContent();
     crossOrigin = true;
     runNextCrossOrigin();
-  } 
+    return;
+  }
+  lastMessage = value;
   window.frames.sameDomain.postMessage(lastMessage, "http://mochi.test:8888");
 }
 
 function runNextCrossOrigin() {
-  try {
-    lastMessage = generator.next();
-  } catch (e) {
+  let {done, value} = generator.next();
+  if (done) {
     SimpleTest.finish();
+    return;
   }
+  lastMessage = value;
   window.frames.crossDomain.postMessage(lastMessage, "http://example.org:8000");
 }
 
diff --git a/dom/workers/test/referrer_worker.html b/dom/workers/test/referrer_worker.html
index 5693fc340885..78ce8a059b3d 100644
--- a/dom/workers/test/referrer_worker.html
+++ b/dom/workers/test/referrer_worker.html
@@ -26,7 +26,7 @@ function finish() {
   // Let window.onerror have a chance to fire
   setTimeout(function() {
     setTimeout(function() {
-      tests.close();
+      tests.return();
       window.parent.postMessage("SimpleTest.finish();", "*");
     }, 0);
   }, 0);
@@ -119,7 +119,7 @@ function checkIndividualResults(aType, aPolicy, aExpected) {
   doXHR(GET_RESULT, onload, onerror);
 }
 
-var tests = (function() {
+var tests = (function*() {
 
   for (var type in testCases) {
     for (var policy in testCases[type]['Referrer-Policy']) {
@@ -137,8 +137,7 @@ var tests = (function() {
     }
   }
 
-  // complete.  Be sure to yield so we don't call this twice.
-  yield finish();
+  finish();
 })();
 </script>
 </body>
diff --git a/dom/workers/test/test_multi_sharedWorker.html b/dom/workers/test/test_multi_sharedWorker.html
index ba028302faf6..63095bfdff23 100644
--- a/dom/workers/test/test_multi_sharedWorker.html
+++ b/dom/workers/test/test_multi_sharedWorker.html
@@ -25,7 +25,7 @@
         const errorMessage = "Error: Expected";
         const errorLineno = 34;
 
-        let testGenerator = (function() {
+        let testGenerator = (function*() {
           SimpleTest.waitForExplicitFinish();
 
           window.addEventListener("message", function(event) {
@@ -228,10 +228,9 @@
           window.removeEventListener("message", sendToGenerator);
 
           SimpleTest.finish();
-          yield undefined;
         })();
 
-        let sendToGenerator = testGenerator.send.bind(testGenerator);
+        let sendToGenerator = testGenerator.next.bind(testGenerator);
 
       </script>
   </head>
diff --git a/dom/workers/test/test_multi_sharedWorker_lifetimes.html b/dom/workers/test/test_multi_sharedWorker_lifetimes.html
index a3f4dc9b5ba5..df12466b695d 100644
--- a/dom/workers/test/test_multi_sharedWorker_lifetimes.html
+++ b/dom/workers/test/test_multi_sharedWorker_lifetimes.html
@@ -19,7 +19,7 @@
         const frameRelativeURL = "multi_sharedWorker_frame.html";
         const storedData = "0123456789abcdefghijklmnopqrstuvwxyz";
 
-        let testGenerator = (function() {
+        let testGenerator = (function*() {
           SimpleTest.waitForExplicitFinish();
 
 	  // Force scrollbar to always be shown.  The scrollbar setting is
@@ -143,10 +143,9 @@
           window.removeEventListener("message", sendToGenerator);
 
           SimpleTest.finish();
-          yield undefined;
         })();
 
-        let sendToGenerator = testGenerator.send.bind(testGenerator);
+        let sendToGenerator = testGenerator.next.bind(testGenerator);
 
       </script>
   </head>
diff --git a/dom/xbl/test/test_bug591198.html b/dom/xbl/test/test_bug591198.html
index 2c7df3613db3..4ed3dc0fefab 100644
--- a/dom/xbl/test/test_bug591198.html
+++ b/dom/xbl/test/test_bug591198.html
@@ -18,10 +18,10 @@ SimpleTest.waitForExplicitFinish();
 
 gen = runTest();
 
-function runTest() {
+function* runTest() {
   let iframe = $('iframe');
   window.addEventListener("message", function(e) {
-    gen.send(JSON.parse(e.data));
+    gen.next(JSON.parse(e.data));
   }, false);
   
   iframe.src = "file_bug591198_inner.html";
@@ -37,7 +37,6 @@ function runTest() {
   is("anonChildCount" in res, false, "no anon children");
 
   SimpleTest.finish();
-  yield undefined;
 }
 
 </script>
diff --git a/dom/xhr/tests/test_XHR.html b/dom/xhr/tests/test_XHR.html
index 143805a9ea5a..ced2ec5ec061 100644
--- a/dom/xhr/tests/test_XHR.html
+++ b/dom/xhr/tests/test_XHR.html
@@ -18,7 +18,7 @@ SimpleTest.waitForExplicitFinish();
 var gen = runTests();
 function continueTest() { gen.next(); }
 
-function runTests() {
+function* runTests() {
 
 var path = "/tests/dom/xhr/tests/";
 
@@ -384,8 +384,6 @@ client.onreadystatechange = function() {
 client.abort();
 
 SimpleTest.finish();
-yield undefined;
-
 } /* runTests */
 </script>
 </pre>
diff --git a/dom/xhr/tests/test_XHRDocURI.html b/dom/xhr/tests/test_XHRDocURI.html
index e3bd1d31114a..73a5846ac968 100644
--- a/dom/xhr/tests/test_XHRDocURI.html
+++ b/dom/xhr/tests/test_XHRDocURI.html
@@ -101,7 +101,7 @@ function testCloneDocURI(aDoc) {
   is(clone.baseURI, aDoc.baseURI, "wrong base (clone)");
 }
 
-function runTest() {
+function* runTest() {
   is(document.baseURI, "http://example.org/", "wrong doc baseURI");
 
   // use content XHR and access URI properties from content privileged script
@@ -504,7 +504,6 @@ function runTest() {
 
   SimpleTest.finish();
   SpecialPowers.removePermission("systemXHR", document);
-  yield undefined;
 }
 
 </script>
diff --git a/dom/xhr/tests/test_XHRSendData.html b/dom/xhr/tests/test_XHRSendData.html
index c210efc9c47d..e15a4345f73e 100644
--- a/dom/xhr/tests/test_XHRSendData.html
+++ b/dom/xhr/tests/test_XHRSendData.html
@@ -46,7 +46,7 @@ function createFiles() {
 
 function continueTest() { gen.next(); }
 
-function runTests() {
+function* runTests() {
 xhr = new XMLHttpRequest();
 xhr.open("GET", "file_XHRSendData_doc.xml", false);
 xhr.send();
@@ -258,7 +258,6 @@ function is_identical_arraybuffer(ab1, ab2) {
 }
 
 SimpleTest.finish();
-yield undefined;
 } /* runTests */
 
 </script>
diff --git a/dom/xhr/tests/test_xhr_progressevents.html b/dom/xhr/tests/test_xhr_progressevents.html
index f22927daff6b..f150925c29b7 100644
--- a/dom/xhr/tests/test_xhr_progressevents.html
+++ b/dom/xhr/tests/test_xhr_progressevents.html
@@ -23,7 +23,7 @@ function log(s) {
 
 function getEvent(e) {
   log("got event: " + e.type + " (" + e.target.readyState + ")");
-  gen.send(e);
+  gen.next(e);
 }
 
 function startsWith(a, b) {
@@ -126,7 +126,7 @@ function bufferToString(buffer) {
   return String.fromCharCode.apply(String, new Uint8Array(buffer));
 }
 
-function runTests() {
+function* runTests() {
   var xhr = new XMLHttpRequest();
   xhr.onprogress = xhr.onload = xhr.onerror = xhr.onreadystatechange = xhr.onloadend = getEvent;
 
@@ -324,7 +324,6 @@ function runTests() {
   }
 
   SimpleTest.finish();
-  yield undefined;
 }
 
 </script>