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diff --git a/dom/base/test/test_bug493881.js b/dom/base/test/test_bug493881.js
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+++ b/dom/base/test/test_bug493881.js
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+/**
+ * Test for Bug 493881: Changes to legacy HTML color properties before the BODY is loaded
+ * should be ignored. Additionally, after BODY loads, setting any of these properties to undefined
+ * should cause them to be returned as the string "undefined".
+ */
+
+SimpleTest.waitForExplicitFinish();
+
+var legacyProps = [
+  "fgColor",
+  "bgColor",
+  "linkColor",
+  "vlinkColor",
+  "alinkColor",
+];
+var testColors = ["blue", "silver", "green", "orange", "red"];
+var rgbTestColors = [
+  "rgb(255, 0, 0)",
+  "rgb(192, 192, 192)",
+  "rgb(0, 128, 0)",
+  "rgb(255, 165, 0)",
+  "rgb(255, 0, 0)",
+];
+var idPropList = [
+  { id: "plaintext", prop: "color" },
+  { id: "body", prop: "background-color" },
+  { id: "nonvisitedlink", prop: "color" },
+  { id: "visitedlink", prop: "color" },
+];
+var initialValues = [];
+
+function setAndTestProperty(prop, color) {
+  var initial = document[prop];
+  document[prop] = color;
+  is(document[prop], initial, "document[" + prop + "] not ignored before body");
+  return initial;
+}
+
+/**
+ * Attempt to set legacy color properties before BODY exists, and verify that such
+ * attempts are ignored.
+ */
+for (let i = 0; i < legacyProps.length; i++) {
+  initialValues[i] = setAndTestProperty(legacyProps[i], testColors[i]);
+}
+
+/**
+ * After BODY loads, run some more tests.
+ */
+addLoadEvent(function () {
+  // Verify that the legacy color properties still have their original values.
+  for (let i = 0; i < legacyProps.length; i++) {
+    is(
+      document[legacyProps[i]],
+      initialValues[i],
+      "document[" + legacyProps[i] + "] altered after body load"
+    );
+  }
+
+  // Verify that legacy color properties applied before BODY are really ignored when rendering.
+  // Save current computed style colors for later use.
+  for (let i = 0; i < idPropList.length; i++) {
+    var style = window.getComputedStyle(
+      document.getElementById(idPropList[i].id)
+    );
+    var color = style.getPropertyValue(idPropList[i].prop);
+    idPropList[i].initialComputedColor = color;
+    isnot(color, rgbTestColors[i], "element rendered using before-body style");
+  }
+  // XXX: Can't get links to visually activate via script events, so can't verify
+  // that the alinkColor property was not applied.
+
+  // Verify that setting legacy color props to undefined after BODY loads will cause them
+  // to be read as the string "undefined".
+  for (let i = 0; i < legacyProps.length; i++) {
+    document[legacyProps[i]] = undefined;
+    is(
+      document[legacyProps[i]],
+      "undefined",
+      "Unexpected value of " + legacyProps[i] + " after setting to undefined"
+    );
+  }
+
+  // Verify that setting legacy color props to undefined led to result
+  // of parsing undefined as a color.
+  for (let i = 0; i < idPropList.length; i++) {
+    var style = window.getComputedStyle(
+      document.getElementById(idPropList[i].id)
+    );
+    var color = style.getPropertyValue(idPropList[i].prop);
+    is(
+      color,
+      "rgb(0, 239, 14)",
+      "element's style should get result of parsing undefined as a color"
+    );
+  }
+
+  // Mark the test as finished.
+  setTimeout(SimpleTest.finish, 0);
+});