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diff --git a/dom/canvas/test/webgl-conf/checkout/conformance2/transform_feedback/unwritten-output-defaults-to-zero.html b/dom/canvas/test/webgl-conf/checkout/conformance2/transform_feedback/unwritten-output-defaults-to-zero.html
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+++ b/dom/canvas/test/webgl-conf/checkout/conformance2/transform_feedback/unwritten-output-defaults-to-zero.html
@@ -0,0 +1,133 @@
+<!--
+Copyright (c) 2019 The Khronos Group Inc.
+Use of this source code is governed by an MIT-style license that can be
+found in the LICENSE.txt file.
+-->
+
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>WebGL Transform Feedback Conformance Tests</title>
+<link rel="stylesheet" href="../../resources/js-test-style.css"/>
+<script src="../../js/js-test-pre.js"></script>
+<script src="../../js/webgl-test-utils.js"></script>
+</head>
+<body>
+<div id="description"></div>
+<canvas id="canvas" style="width: 50px; height: 50px;"> </canvas>
+<div id="console"></div>
+<script id="vshader" type="x-shader/x-vertex">#version 300 es
+in vec4 in_data;
+uniform int flag;
+out vec4 out_data;
+void main(void) {
+    if (flag > 0) {
+        out_data = in_data + vec4(2.0, 3.0, 4.0, 5.0);
+    }
+}
+</script>
+<script id="fshader" type="x-shader/x-fragment">#version 300 es
+precision mediump float;
+out vec4 out_color;
+void main(void) {
+    out_color = vec4(1.0, 1.0, 1.0, 1.0);
+}
+</script>
+<script>
+"use strict";
+description("This test verifies if an output variable is specified to be streamed to a transform feedback buffer but not actually written, the value defaults to 0.");
+
+debug("");
+
+var wtu = WebGLTestUtils;
+var canvas = document.getElementById("canvas");
+var gl = wtu.create3DContext(canvas, null, 2);
+
+if (!gl) {
+    testFailed("WebGL context does not exist");
+} else {
+    testPassed("WebGL context exists");
+
+    debug("");
+    debug("Testing transform feedback works fine");
+    runTest(1);
+
+    debug("");
+    debug("Testing unwritten output variables default to zero");
+    runTest(0);
+}
+
+function runTest(flag) {
+    var in_data = [
+        1.0, 2.0, 3.0, 4.0,
+        2.0, 4.0, 8.0, 16.0,
+        0.75, 0.5, 0.25, 0.0
+    ];
+
+    var in_buffer = gl.createBuffer();
+    gl.bindBuffer(gl.ARRAY_BUFFER, in_buffer);
+    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(in_data), gl.STATIC_DRAW);
+
+    var out_buffer = gl.createBuffer();
+    gl.bindBuffer(gl.TRANSFORM_FEEDBACK_BUFFER, out_buffer);
+    gl.bufferData(gl.TRANSFORM_FEEDBACK_BUFFER, Float32Array.BYTES_PER_ELEMENT * in_data.length, gl.STATIC_DRAW);
+
+    // Create the transform feedback program
+    var program = wtu.setupTransformFeedbackProgram(gl, ["vshader", "fshader"],
+        ["out_data"], gl.SEPARATE_ATTRIBS,
+        ["in_data"]);
+    var loc = gl.getUniformLocation(program, "flag");
+    if (!program || !loc) {
+        testFailed("Fail to set up the program");
+        return;
+    }
+    gl.uniform1i(loc, flag);
+    wtu.glErrorShouldBe(gl, gl.NO_ERROR, "Set up program should succeed");
+
+    // Draw the the transform feedback buffers
+    var tf = gl.createTransformFeedback();
+
+    gl.enableVertexAttribArray(0);
+    gl.bindBuffer(gl.ARRAY_BUFFER, in_buffer);
+    gl.vertexAttribPointer(0, 4, gl.FLOAT, false, 16, 0);
+
+    gl.bindTransformFeedback(gl.TRANSFORM_FEEDBACK, tf);
+    gl.bindBufferBase(gl.TRANSFORM_FEEDBACK_BUFFER, 0, out_buffer);
+
+    gl.enable(gl.RASTERIZER_DISCARD);
+    gl.beginTransformFeedback(gl.POINTS);
+
+    gl.drawArrays(gl.POINTS, 0, 3);
+
+    gl.endTransformFeedback();
+    gl.disable(gl.RASTERIZER_DISCARD);
+
+    gl.bindBufferBase(gl.TRANSFORM_FEEDBACK_BUFFER, 0, null);
+
+    // Verify the output buffer contents
+    var expected_data;
+    if (flag > 0) {
+        expected_data = [
+            3.0, 5.0, 7.0, 9.0,
+            4.0, 7.0, 12.0, 21.0,
+            2.75, 3.5, 4.25, 5.0
+        ];
+    } else {
+        expected_data = [
+            0.0, 0.0, 0.0, 0.0,
+            0.0, 0.0, 0.0, 0.0,
+            0.0, 0.0, 0.0, 0.0
+        ];
+    }
+    gl.bindBuffer(gl.TRANSFORM_FEEDBACK_BUFFER, out_buffer);
+    wtu.checkFloatBuffer(gl, gl.TRANSFORM_FEEDBACK_BUFFER, expected_data);
+}
+
+debug("");
+var successfullyParsed = true;
+</script>
+<script src="../../js/js-test-post.js"></script>
+
+</body>
+</html>