diff --git a/sdk/tests/conformance/textures/misc/texture-active-bind.html b/sdk/tests/conformance/textures/misc/texture-active-bind.html
index 5f7d74191d..1aa5bf3858 100644
--- a/sdk/tests/conformance/textures/misc/texture-active-bind.html
+++ b/sdk/tests/conformance/textures/misc/texture-active-bind.html
@@ -50,6 +50,20 @@
   texCoord = texCoord0;
 }
 </script>
+<script id="trivial-vs" type="text/plain">
+void main()
+{
+  gl_Position = vec4(0,0,0,1);
+}
+</script>
+<script id="tex-point-fs" type="text/plain">
+precision mediump float;
+uniform sampler2D uSampler;
+void main()
+{
+  gl_FragColor = texture2D(uSampler, vec2(0));
+}
+</script>
 <script>
 "use strict";
 var gl;
@@ -128,6 +142,51 @@
     var y = Math.floor(ii / 2);
     wtu.checkCanvasRect(gl, x, y, 1, 1, colors[ii]);
   }
+
+  debug("");
+  debug("Swizzle applied to correct ActiveTexture index");
+
+  {
+    const prog = wtu.setupProgram(
+        gl,
+        ["trivial-vs", "tex-point-fs"]);
+    prog.uSampler = gl.getUniformLocation(prog, "uSampler");
+    gl.useProgram(prog);
+    gl.viewport(0, 0, 1, 1);
+    gl.activeTexture(gl.TEXTURE0);
+    wtu.glErrorShouldBe(gl, gl.NO_ERROR);
+
+    const tex0_rgba8 = gl.createTexture();
+    gl.bindTexture(gl.TEXTURE_2D, tex0_rgba8);
+    const tex0_rgba8_data = new Uint8Array([10, 20, 30, 40]);
+    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE, tex0_rgba8_data);
+
+    const tex2_a8 = gl.createTexture();
+    gl.bindTexture(gl.TEXTURE_2D, tex2_a8);
+    gl.texImage2D(gl.TEXTURE_2D, 0, gl.ALPHA, 1, 1, 0, gl.ALPHA, gl.UNSIGNED_BYTE, null);
+
+    window.control = new Uint8Array(4);
+    window.after_swizzle_applied = new Uint8Array(4);
+
+    gl.bindTexture(gl.TEXTURE_2D, tex0_rgba8);
+    gl.drawArrays(gl.POINTS, 0, 1);
+    gl.readPixels(0, 0, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, window.control);
+    shouldBeString("window.control", tex0_rgba8_data.toString());
+
+    gl.activeTexture(gl.TEXTURE2);
+    gl.bindTexture(gl.TEXTURE_2D, tex2_a8);
+    gl.uniform1i(prog.uSampler, 2);
+    gl.activeTexture(gl.TEXTURE0);
+    gl.drawArrays(gl.POINTS, 0, 1);
+    // Firefox would apply the A8-on-R8 swizzle to whatever tex-unit was active.
+
+    gl.uniform1i(prog.uSampler, 0);
+    gl.drawArrays(gl.POINTS, 0, 1);
+    gl.readPixels(0, 0, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, window.after_swizzle_applied);
+    shouldBeString("window.after_swizzle_applied", tex0_rgba8_data.toString());
+    // Firefox would then get 0,0,0,10 here, as the [ZERO,ZERO,ZERO,RED] swizzle was applied to our
+    // 10,20,30,40 texture.
+  }
 }
 
 init();
diff --git a/sdk/tests/js/js-test-pre.js b/sdk/tests/js/js-test-pre.js
index e1e70188fb..ece0adfcc1 100644
--- a/sdk/tests/js/js-test-pre.js
+++ b/sdk/tests/js/js-test-pre.js
@@ -373,6 +373,16 @@ function evalAndLog(_a)
   return _av;
 }
 
+function shouldBeString(evalable, expected) {
+    const val = eval(evalable);
+    const text = evalable + " should be " + expected + ".";
+    if (val == expected) {
+        testPassed(text);
+    } else {
+        testFailed(text + " (was " + val + ")");
+    }
+}
+
 function shouldBe(_a, _b, quiet)
 {
     if (typeof _a != "string" || typeof _b != "string")