diff --git a/dom/browser-element/mochitest/async.js b/dom/browser-element/mochitest/async.js
index 269a04811405..dfbc3a0f2406 100644
--- a/dom/browser-element/mochitest/async.js
+++ b/dom/browser-element/mochitest/async.js
@@ -62,11 +62,7 @@
               .then(
                 result => step(gen.next(result)),
                 error => {
-                  try {
-                    step(gen.throw(error));
-                  } catch (err) {
-                    throw err;
-                  }
+                  step(gen.throw(error));
                 }
               )
               .catch(err => reject(err));
diff --git a/dom/canvas/test/test_2d_composite_canvaspattern_setTransform.html b/dom/canvas/test/test_2d_composite_canvaspattern_setTransform.html
index 6e46774d04da..2c525c2362e8 100644
--- a/dom/canvas/test/test_2d_composite_canvaspattern_setTransform.html
+++ b/dom/canvas/test/test_2d_composite_canvaspattern_setTransform.html
@@ -60,8 +60,8 @@ function runTests() {
  try {
   test_2d_canvaspattern_setTransform();
  } catch(e) {
-  throw e;
   ok(false, "unexpected exception thrown in: test_2d_canvaspattern_setTransform");
+  throw e;
  }
  SimpleTest.finish();
 }
@@ -75,4 +75,3 @@ document.all;
 window.p = new Path2D();
 
 </script>
-
diff --git a/dom/canvas/test/test_canvas.html b/dom/canvas/test/test_canvas.html
index 95ceda4db3c0..9426667bfc7f 100644
--- a/dom/canvas/test/test_canvas.html
+++ b/dom/canvas/test/test_canvas.html
@@ -25606,14 +25606,14 @@ function runTests() {
  try {
   test_getImageData_after_zero_canvas();
  } catch(e) {
-  throw e;
   ok(false, "unexpected exception thrown in: test_getImageData_after_zero_canvas");
+  throw e;
  }
  try {
   test_opaque();
  } catch(e) {
-  throw e;
   ok(false, "unexpected exception thrown in: test_opaque");
+  throw e;
  }
  try {
   test_2d_transformation_reset_transform();
@@ -25764,8 +25764,8 @@ function runTests() {
  try {
    test_2d_clearRect_testdoubleprecision();
  } catch(e) {
-   throw e;
    ok(false, "unexpected exception thrown in: test_2d_clearRect_testdoubleprecision");
+   throw e;
  }
 
  //run the asynchronous tests
diff --git a/dom/canvas/test/test_canvas_focusring.html b/dom/canvas/test/test_canvas_focusring.html
index ef7cddd2e895..0e9566ac2914 100644
--- a/dom/canvas/test/test_canvas_focusring.html
+++ b/dom/canvas/test/test_canvas_focusring.html
@@ -60,8 +60,8 @@ function runTests() {
  try {
   test_drawFocusIfNeeded_canvas();
  } catch(e) {
-  throw e;
   ok(false, "unexpected exception thrown in: test_drawFocusIfNeeded_canvas");
+  throw e;
  }
 
  SpecialPowers.setBoolPref("canvas.focusring.enabled", false);
diff --git a/dom/canvas/test/test_hitregion_canvas.html b/dom/canvas/test/test_hitregion_canvas.html
index 49cefb0b46c6..0ac826164377 100644
--- a/dom/canvas/test/test_hitregion_canvas.html
+++ b/dom/canvas/test/test_hitregion_canvas.html
@@ -72,8 +72,8 @@ function runTests() {
  try {
   test_hitregions();
  } catch(e) {
-  throw e;
   ok(false, "unexpected exception thrown in: test_hitregions");
+  throw e;
  }
  SimpleTest.finish();
 }
diff --git a/dom/websocket/tests/websocket_helpers.js b/dom/websocket/tests/websocket_helpers.js
index 24ef3ba4a43a..18f9f5a835f5 100644
--- a/dom/websocket/tests/websocket_helpers.js
+++ b/dom/websocket/tests/websocket_helpers.js
@@ -28,23 +28,19 @@ function ignoreError(e) {}
 function CreateTestWS(ws_location, ws_protocol) {
   var ws;
 
-  try {
-    if (ws_protocol == undefined) {
-      ws = new WebSocket(ws_location);
-    } else {
-      ws = new WebSocket(ws_location, ws_protocol);
-    }
-
-    ws._testNumber = current_test;
-    ok(true, "Created websocket for test " + ws._testNumber + "\n");
-
-    ws.onerror = function(e) {
-      ok(false, "onerror called on test " + e.target._testNumber + "!");
-    };
-  } catch (e) {
-    throw e;
+  if (ws_protocol == undefined) {
+    ws = new WebSocket(ws_location);
+  } else {
+    ws = new WebSocket(ws_location, ws_protocol);
   }
 
+  ws._testNumber = current_test;
+  ok(true, "Created websocket for test " + ws._testNumber + "\n");
+
+  ws.onerror = function(e) {
+    ok(false, "onerror called on test " + e.target._testNumber + "!");
+  };
+
   return ws;
 }